BUSHEHR, Iran — Iranian and Russian engineers carried out a test-run of Iran's first nuclear power plant Wednesday, a major step toward starting up a facility that the U.S. once hoped to prevent because of fears over Tehran's nuclear ambitions.
Washington worried Iran would turn spent fuel from the plant's reactor into plutonium, which could then be used to build a nuclear warhead, and U.S. officials pressured Moscow for years to stop helping Iran build the electricity-generating facility.
American opposition to the plant eased when Iran agreed in 2005 to return spent fuel to Russia to ensure it can't be reprocessed into plutonium. Russia is providing enriched uranium fuel for the plant in the southern port city of Bushehr.
But the U.S. and its allies say there are deep questions about whether Iran intends to use other parts of its nuclear program to develop atomic weapons. Tehran denies that.
The United States said Wednesday that the fuel deal with Russia shows Tehran does not need the most controversial part of its nuclear program _ facilities to produce its own enriched uranium.
The arrangement with Russia is "an appropriate mechanism for Iran to see the benefits of the peaceful use of nuclear energy," State Department spokesman Robert A. Wood said in Washington. "It also demonstrates that Iran does not need to develop any kind of indigenous uranium enrichment capacity."
The U.N. Security Council, the U.S. and other countries have demanded that Iran suspend enrichment because the process not only can produce fuel for a reactor, but can be used to develop highly enriched uranium needed to make nuclear bombs.
Iran denies it is seeking to build atomic weapons, and says it has a right to produce its own fuel for several nuclear power plants it plans to build. It says relying on imported fuel for its entire reactor program would leave it vulnerable to cutoffs as political pressure.
Iranian officials on Wednesday claimed further progress in expanding the uranium enrichment program, saying the number of centrifuges operating at its enrichment plant has increased to 6,000, up from 5,000 in November.
In Israel, which has been one of the most vocal nations accusing Iran of seeking to develop atomic weapons, Foreign Ministry spokesman Yigal Palmor said the tests at Bushehr "should be understood as very bad news for the whole of the international community" because it shows Iran's nuclear program is progressing.
Israeli Defense Minister Ehud Barak warned that "time is slipping through our fingers" in preventing Iran from developing a weapon. He called for "harsh sanctions" and a "willingness to consider other options" if sanctions don't succeed _ a reference to military action.
"We do not take any option off the table regarding to Iran's nuclear program," he said.
Iran has warned of strong retaliation _ including stopping oil shipments through the Persian Gulf or hitting U.S. bases there _ if Israel or the United States carries out military strikes on its nuclear facilities.
The tests at Bushehr brought the power station closer to full operation. But Iran and Russia's top nuclear officials, touring the facility Wednesday, would not say when exactly electricity production would begin.
The opening of the 1,000-megawatt, light-water reactor, under construction for 14 years, has repeatedly been delayed by construction and supply glitches. Russian began shipping fuel for the plant in 2007. Iran has said it aims to operate the reactor by the end of the year.
The tests "could take between four and seven months," Iran's nuclear chief, Vice President Gholam Reza Aghazadeh, told reporters. "We are approaching full exploitation of this plant."
Russian nuclear head Sergei Kiriyenko said that Bushehr had "remarkable progress in recent months" and that technicians were "approaching the final stage."
Scientists at the plant are carrying out a computer run of the equipment to ensure there are no malfunctions when it begins real operations. No electricity is produced during the testing.
In the first stage of the test, technicians began 10 days ago loading "virtual fuel" into the reactor. The test fuel consists of lead, which imitates the density of enriched uranium. Once the fuel is loaded, the equipment will be tested.
Aghazadeh said the test was going well and engineers told him they expected no problems.
The U.N. Security Council has imposed three rounds of financial sanctions on Iran over the enrichment dispute, but Tehran has refused to suspend that work.
In the enrichment process, uranium gas is pumped through a series of centrifuges and spun at supersonic speeds to remove impurities. A low level of enrichment produces reactor fuel, but more highly enriched uranium can be used for the core a warhead.
Aghazadeh said 6,000 centrifuges are now "operating" at Iran's enrichment facility in the town of Natanz. He said Iran hopes to install over 50,000 centrifuges there over the next five years.
Iran says it intends to use the enriched uranium in its first domestically built nuclear power plant, which is scheduled to start operating in 2016 in the town of Darkhovin.
Aghazadeh said delaying enrichment would mean a delay in opening that reactor. "We are doing what we need to do in Natanz on the basis of a specific time schedule," he said at a news conference.
In a report last week, the U.N. nuclear watchdog, the International Atomic Energy Agency, said Iran had about 4,000 centrifuges actively enriching and 1,600 more "under vacuum," which means they are operating but not yet being fed uranium gas to spin.
An IAEA official said the Iranian numbers appeared to roughly tally with the agency's count, including machines under vacuum. The official, who insisted on anonymity in return for discussing an IAEA member nation, declined to comment on the Bushehr testing.
The Bushehr project dates backs to 1974, when Iran's U.S.-backed Shah Mohammed Reza Pahlavi contracted with the German company Siemens to build the reactor. The company withdrew from the project after the 1979 Islamic revolution toppled the shah.
In 1992, Iran signed an agreement with Russia to complete the project and work began in 1995.
Associated Press writers Matti Friedman in Jerusalem and George Jahn in Vienna contributed to this report.