BAGHDAD — Talks between Iran and six world powers snagged Wednesday over dueling proposals concerning Tehran's nuclear program, a tug-of-war that pits international concerns about the Islamic Republic's potential to build atomic weapons against enforcing crippling sanctions on its people.

The daylong back-and-forth in Baghdad focused largely on whether the current enrichment level of Iran's uranium production is a red line the U.S. and other powers will not permit for fear it could become warhead-grade material.

At stake is the threat an Iran armed with nuclear weapons could pose to its neighbors. The U.S. and Israel have indicated readiness to attack Iran if diplomacy and sanctions fail to curb its nuclear program. Both suspect that Iran is aiming to build nuclear weapons, and Israel believes it would be a prime target.

Iran insists its nuclear program is peaceful.

The impasse threatened to dissolve the most hopeful chance of detente in nearly a decade, although both sides agreed to continue negotiations into Thursday.

"The international community hasn't done something wrong here – we haven't created a suspicious nuclear weapons program that the world doesn't know the answers to. Iran has," a senior U.S. official said early Thursday after the grueling day of discussions that, at times, appeared on the verge of breaking down. "They are the party who has acted to create concerns in the international community."

However, the official said, the negotiations remain in the beginning of a careful and drawn-out process. "We certainly are not at the end of it," said the U.S. official who spoke on condition of anonymity to discuss the talks more candidly.

Western negotiators presented a package Wednesday that called on Tehran to place a freeze on its enrichment of uranium to 20 percent, considered a short technical step away from bomb grade. In exchange they offered benefits, including medical isotopes, some nuclear safety cooperation and spare parts for civilian airliners, much needed in Iran.

But they snubbed Iranian calls for an immediate easing of significant economic sanctions imposed on Tehran for flouting U.N. Security Council resolutions that demand the suspension of all enrichment.

Iran brought a potent bargaining chip to the table, tentatively agreeing on the eve of the negotiations to allow U.N. inspectors into a military complex suspected of conducting nuclear arms-related tests.

The gesture was seen as an attempt to head off painful July 1 sanctions on its oil exports to lucrative European markets. U.S. and European measures have targeted Iran's oil exports – its chief revenue source – and effectively blocked the country from international banking networks.

Diplomats from the six world powers have refused to consider postponing the new harsher sanctions, although the U.S. official said some restrictions could be removed as part of an agreement.

The talks are seen only as a small step forward in a delicate negotiating process that likely will unfold over months. That would likely bring objections from Israel, which claims that Iran is only trying to buy time to keep its nuclear fuel labs in full operation.

But a delay could allow U.S. and European allies to tone down threats of military action – despite calls Wednesday from a hawkish alliance of U.S. senators who urged negotiators to take a hard line against Iran "to leave no doubt that the window for diplomacy is closing."

"The Iranian regime's long record of deceit and defiance should make us extremely cautious about its willingness to engage in good-faith diplomacy," Republican Sens. John McCain and Lindsey Graham, and Independent Joe Lieberman, wrote in Wednesday's editions of The Wall Street Journal. "The U.S. must be prepared, if necessary, to use military force to stop Iran from getting a nuclear-weapons capability."

The Baghdad meetings opened with the so-called 5+1 group – the permanent U.N. Security Council members, the United States, Russia, China, Britain and France, plus Germany – putting forward a proposal aimed at putting a cap on Iran's growing stockpile of uranium enriched to 20 percent. Iran says the uranium is for fuel for medical reactors, but Western diplomats say Tehran already has many times more than it needs, and that moving from 20 percent to bomb-grade purity is a relatively quick and easy process.

The U.S. official said it is too early in the negotiations to discuss whether world powers would agree to let Tehran maintain a lesser percentage of uranium enrichment. "It's premature to have that discussion," the official said.

Mike Mann, spokesman for the head of the European Union delegation that is leading the talks, suggested that any rollback in sanctions was unlikely in the Baghdad talks. He called the upcoming sanctions a "matter of the law and they will come into force when they come into force."

Iran offered a counterproposal that includes "nuclear and non-nuclear issues," according to the member of its negotiating team. The official would not discuss details of the plan but said it was to be discussed in private meetings with diplomats from the European Union and China, an Iranian ally.

Iran's top officials, including Supreme Leader Ayatollah Ali Khamenei, have repeatedly said that Iran does not seek nuclear arms and have called such weapons against Islamic principles.

During a visit to western Iran on Wednesday, President Mahmoud Ahmadinejad evoked Khamenei's belief that "production and use of weapons of mass destruction is forbidden" by Islam.

"There is no room for these weapons in Iran's defense doctrine," he said at a gathering to commemorate victims of Iraqi chemical weapons during the 1980-88 war with Saddam Hussein's Iraq.

Even so, Iran is sticking to its right to enrich uranium as a signatory of U.N. nuclear treaties. The high-enriched uranium is far above the level needed for energy-producing reactors, but is used in medical research. Iran claims its nuclear program is only for electricity and medical applications.

Earlier this week, Tehran tentatively agreed to allow the U.N. International Atomic Energy Agency inspect the Parchin military complex southeast of Tehran. That's where the U.N. believes Iran ran explosive tests in 2003 needed to set off a nuclear charge. Tehran says Parchin is not a nuclear site.

The Iranian envoys entered the talks sorely wanting to lessen, or at least delay, an EU decision to cut all crude oil imports from Iran that are set to take effect July 1. The 27-nation EU accounts for just 18 percent of Iran's total oil exports.

Earlier this week, the U.S. Senate backed proposals for further sanctions on Iran, including requiring companies listed on U.S. stock exchanges to disclose any Iran-related business. U.S. and European measures already have targeted Iran's oil exports – its chief revenue source – and effectively blocked the country from international banking networks.

Oil fell to a seven-month low near $91 a barrel Wednesday on hopes of progress in the talks.

If the July 1 sanctions start as planned, Iran's Economy Minister Shamseddin Hossein predicted they will backfire, warning this week that Europe should expect a crude oil price of $160 a barrel should the embargo remain in place.

That puts a ticking clock on a negotiations process that, for all its bluffing and brinksmanship, may drag on "for several weeks, if not for several months," said Bruno Tertrais, senior research fellow at the Foundation for Strategic Research in Paris.

"There will be incentives to not rush toward any kind of deal," Tertrais said.

___

Associated Press writers Brian Murphy in Dubai, United Arab Emirates, and Nasser Karimi in Tehran, Iran, contributed to this report.

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  • <em>In this Saturday, Nov. 12, 2011 photo, Iranian women and a man weave carpet in a workshop in Qom, 78 miles (125 kilometers) south of the capital Tehran, Iran. (AP Photo/Vahid Salemi)</em><br><br> Initial sanctions were imposed after Iranian students stormed the U.S. embassy and took diplomats hostage in 1979. Iranian products cannot be imported into the United States apart from small gifts, information material, food and some carpets.

  • <em>Former President Bill Clinton addresses the audience during the opening night dinner of the World Summit of Nobel Peace Laureates at the Field Museum Monday, April 23, 2012, in Chicago. (AP Photo/Charles Rex Arbogast)</em><br><br> In 1995, President Bill Clinton issued executive orders preventing U.S. companies from investing in Iranian oil and gas and trading with Iran. The same year, Congress passed a law imposing sanctions on foreign companies investing more than $20 million a year in Iran's energy sector.

  • <em>In this Thursday, Oct. 30, 2008 file photo, an Iranian money changer holds currency with Ayatollah Ruhollah Khomeini's image in Tehran, Iran. (AP Photo/Hasan Sarbakhshian, File)</em><br><br> In October 2007, Washington imposed sanctions on three Iranian banks and branded the Islamic Revolutionary Guards Corps a proliferater of weapons of mass destruction. The Treasury has since added numerous other Iranian banks to its blacklist. The Treasury has identified about 20 petroleum and petrochemical companies as being under Iranian government control, an action that put them off-limits to U.S. businesses under the trade embargo.

  • <em>This photo shows a branch of Iranian Bank Tejarat in Tehran on January 24, 2012 upon which the US Treasury announced sanctions claiming all of the Islamic Republic's major state-owned banks have now been subjected to punitive measures. (ATTA KENARE/AFP/Getty Images)</em><br><br> Congress approved tough new unilateral sanctions on June 24, 2010, aimed at squeezing Iran's energy and banking sectors. The new law imposed penalties on companies that supply Iran with refined petroleum products worth more than $5 million a year. It also effectively deprived foreign banks of access to the U.S. financial system if they did business with Iranian banks or the Revolutionary Guards.

  • <em>Oil workers gather by an oil well operated by Venezuela's state-owned oil company PDVSA in Morichal, Venezuela, on July 28, 2011. (RAMON SAHMKOW/AFP/Getty Images)</em><br><br> In May 2011, the United States announced new sanctions on Venezuela's state oil company, PDVSA, and six other smaller oil and shipping firms for trading with Iran in violation of the U.S. ban, prompting fury from Hugo Chavez's government.

  • June 2011

    <em>Members of Iran's paramilitary Basij militia parade in front of the former US embassy in Tehran on November 25, 2011 to mark the national Basij week. (ATTA KENARE/AFP/Getty Images)</em><br><br> On June 11, it announced new sanctions on the Revolutionary Guards, the Basij Resistance Force, and Iran's law enforcement forces. The sanctions froze any of the targets' assets under U.S. jurisdiction and barred U.S. persons and institutions from dealing with them.

  • <em>Secretary of State Hillary Clinton and Treasury Secretary Timothy Geithner (L) announce new sanctions against Iran at the State Department on November 21, 2011 in Washington, DC. (Photo by Mark Wilson/Getty Images)</em><br><br> On Nov. 21 the United States named Iran as an area of "primary money-laundering concern", a step designed to dissuade non-U.S. banks from dealing with it. The United States also blacklisted 11 entities suspected of aiding its nuclear programmes and expanded sanctions to target companies that aid its oil and petrochemical industries.

  • <em>US President Barack Obama (C) greets guests after speaking on nuclear security, touching on subjects from terrorism to Iran and North Korea, during a visit to Hankuk University of Foreign Studies in Seoul on March 26, 2012. (SAUL LOEB/AFP/Getty Images)</em><br><br> On Dec. 31, 2011, President Barack Obama signed into law a defense funding bill that imposed sanctions on financial institutions dealing with Iran's central bank, which is the main conduit for oil revenues. Sanctioned institutions would be frozen out of the U.S. financial markets.

  • <em>Hostesses stand in front of the construction site of the Saudi Basic Industries Corp. (SABIC) Technology Centre and Greater China Headquarters in Shanghai, China Friday, April 6, 2012. (AP Photo/Eugene Hoshiko)</em><br><br> On Jan. 13, 2012 the United States extended sanctions to Chinese state-run energy trader Zhuhai Zhenrong Corp, which it said was Iran's largest supplier of refined petroleum products. It also imposed sanctions on Singapore's Kuo Oil Pte Ltd and United Arab Emirates-based FAL Oil Company Ltd.

  • <em>Members of Iranian Revolutionary Guards attend a ceremony at the mausoleum of the late revolutionary founder Ayatollah Khomeini, commemorating 33rd anniversary of his return from exile after 14 years, and the 1979 Islamic Revolution which toppled pro-US Shah Mohammad Reza Pahlavi, just outside Tehran, Iran, Wednesday, Feb. 1, 2012. (AP Photo/Vahid Salemi)</em><br><br> The United States exempted Japan and 10 European Union nations from financial sanctions on March 20 because they had significantly cut purchases of Iranian oil, but Iran's top customers China and India remain at risk of such steps. On March 28 the Treasury set additional sanctions against Iranian engineering firms with ties to the Revolutionary Guards, as well as individuals and shipping companies with ties to the Islamic Republic of Iran Shipping Lines (IRISL).

  • <em>In this Sept. 27, 2000 file photo, an Iranian oil worker repairs a pipe at an oil refinery in Tehran. (AP Photo/Vahid Salemi, File)</em><br><br> On May 21 the Senate approved the latest tightening of sanctions on Iran's oil trade.

  • <em>In this Jan. 19, 2012 file photo, fishing boats are seen in front of oil tankers on the Persian Gulf waters, south of the Strait of Hormuz, offshore the town of Ras Al Khaimah in United Arab Emirates. (AP Photo/Kamran Jebreili)</em><br><br> On Aug. 12, 2010 the EU banned the creation of joint ventures with enterprises in Iran engaged in the oil and natural gas industries. Member states must prohibit the provision of insurance and re-insurance to the government of Iran. The import and export of arms and equipment that could contribute to uranium enrichment, or have a "dual use", is banned. The sanctions forbid the sale, supply or transfer of energy equipment and technology used by Iran for exploration and production or for refining or liquefying natural gas. The EU expects the effects of the sanctions to increase over time as existing parts wear out.

  • <em>EU foreign policy chief Catherine Ashton speaks during a media conference after a meeting of EU foreign ministers at the EU Council building in Brussels on Monday, Jan. 23, 2012. (AP Photo/Virginia Mayo)</em><br><br> In May 2011, EU foreign ministers added 100 new entities to a list of companies and people affected, including those owned or controlled by IRISL. Last October, the EU imposed sanctions on 29 people, extending the list targeting individuals associated with human rights violations to 61. On Dec. 1, the EU added 180 Iranians and entities to a sanctions blacklist that imposes asset freezes and travel bans on those involved in the nuclear program.

  • <em>In this March 13, 2008 file photo, gold coins and bars are shown at California Numismatic Investments in Inglewood, Calif. (AP Photo/Nick Ut, File)</em><br><br> On Jan. 23, 2012 the EU placed an immediate ban on all new contracts to import, purchase or transport Iranian crude oil and petroleum products. EU countries with existing contracts to buy oil and petroleum products were allowed to honor them until July 1. The EU also agreed to freeze the assets of Iran's central bank and ban trade in gold and other precious metals with the bank and state bodies.

  • <em>British Ambassador to the UN Mark Lyall Grant (C) speaks during a vote on broader military and financial sanctions on Iran over its suspect nuclear program during a UN Security Council at the UN headquarters June 9, 2010 in New York. (EMMANUEL DUNAND/AFP/Getty Images)</em><br><br> The Security Council has imposed four sets of sanctions on Iran, in December 2006, March 2007, March 2008 and June 2010. The first covered sensitive nuclear materials and froze the assets of Iranian individuals and companies linked with the nuclear program.

  • <em>A military truck carries a Sejil rocket as it is paraded during the annual Army Day military parade in Tehran on April 17, 2012. (ATTA KENARE/AFP/Getty Images)</em><br><br> The second included new arms and financial sanctions. It extended an asset freeze to 28 more groups, companies and individuals engaged in or supporting sensitive nuclear work or the development of ballistic missiles.

  • <em>Iranian President Mahmoud Ahmadinejad adjusts his goggles as he tours an exhibition on laser technology in Tehran on February 7, 2010. (ATTA KENARE/AFP/Getty Images)</em><br><br> The third, in 2008, increased travel and financial curbs on individuals and companies. It expanded a partial ban on trade in items with both civilian and military uses to cover sales of all such technology to Iran.

  • <em>A street money exchanger, puts US dollars in a plastic bag, in Ferdowsi St. in downtown Tehran, Iran, Wednesday, Dec. 21, 2011. (AP Photo/Vahid Salemi)</em><br><br> A Security Council resolution passed on June 9, 2010, called for measures against new Iranian banks abroad if a connection to the nuclear or missile programmes was suspected.

  • <em>Soldiers of the Iranian Revolutionary Guard walk past a satirical drawing of Statue of Liberty on the wall of the former US Embassy in Tehran, Iran, Friday, Nov. 25, 2011. (AP Photo/Vahid Salemi)</em><br><br> It expanded a U.N. arms embargo against Tehran and blacklisted three firms controlled by IRISL and 15 belonging to the Revolutionary Guards. The resolution called for the setting up of a cargo inspection regime.