By Michelle Nichols

UNITED NATIONS, Sept 4 (Reuters) - Syria's conflict has taken a brutal turn with other countries arming both sides, spreading misery and risking "unintended consequences as the fighting intensifies and spreads," U.N. chief Ban Ki-moon told the U.N. General Assembly on Tuesday.

The United Nations and Western officials have accused Iran of supplying weapons to Syria's pro-government forces, while Damascus has accused Qatar and Saudi Arabia of arming rebels determined to topple President Bashar al-Assad.

"This conflict has taken a particularly brutal turn," Ban said of the 17-month crisis. "The continuing militarization of the conflict is deeply tragic and highly dangerous."

"Those who provide arms to either side are only contributing to further misery - and the risk of unintended consequences as the fighting intensifies and spreads," he said.

A U.N. Security Council panel of independent experts that monitors sanctions against Iran has uncovered several examples of Iran transferring arms to Syria's government. The United States and Britain say they are providing non-lethal assistance to Syria's rebels such as communications equipment but not arms.

"The conflict is intensifying," Ban said. "The longer it goes on, the more difficult it will be to contain. The more difficult it will be to find a political solution. The more challenging it will be to rebuild the country and the economy."

The 193-nation General Assembly last month overwhelmingly approved a non-binding resolution, which expressed "grave concern" at the escalation of violence in Syria and condemned the U.N. Security Council for its failure to take strong action.

As Syria spirals deeper into civil war, the Security Council has been paralyzed on taking strong action as Russia and China have blocked three Western-backed resolutions that criticized Assad and threatened sanctions. A council meeting on Thursday on the crisis achieved nothing new.

"How many children will attend the funerals of their parents; how many parents will weep at the funerals of their children, before all parties agree to end the violence and destruction?" Ban said.

"The Syrian people have waited too long," he said. "And now the entire region is being engulfed by the complex dynamics of the conflict."

UNITY MISSING

The new U.N.-Arab League mediator, Lakhdar Brahimi, who took up the role on Saturday and described his bid to broker peace as "nearly impossible," also briefly addressed the U.N. assembly.

"The death toll is staggering, the destruction is reaching catastrophic proportions and the suffering is immense," Brahimi said. "I am looking forward to my visit to Damascus in a few days time, and ... to all the countries who are in a position to help the Syrian-led political process become a reality."

Veteran Algerian diplomat Brahimi replaced Kofi Annan as the international mediator on the Syrian conflict. Annan had blamed the Security Council impasse for hampering his six-month bid to broker peace and leading to his decision to step down.

Syria's U.N. envoy Bashar Ja'afari said that Damascus was "open-minded and fully committed to the mission of Mr Brahimi in his endeavors to put an end to violence and find a Syrian-led political solution to the crisis."

"I'm calling on all member states, particularly those with direct influence .... on the parties rejecting political dialogue and the cessation of violence, I'm calling on them to follow in the footsteps of the government of Syria and seriously extend a helping hand to Mr Lakhdar Brahimi," Ja'afari said.

Ban described Brahimi's task as "daunting, but not insurmountable" and said that what was missing in international efforts to end the conflict was "a unity of effort that will have an impact on the ground."

Iran said last week it will form a team with other non-aligned countries to explore solutions to the crisis, while the United States has said it will turn to alternatives such as the "Friends of Syria" grouping of allied countries to pressure Assad after the Security Council's failure to act.

The United Nations says nearly 20,000 people have been killed in the conflict, which was sparked by a popular uprising against Assad.

Ban said the humanitarian situation was "grave and deteriorating" and the international aid response was constrained by a lack of funding. A $180 million international appeal was only half-funded, he said.

Assad pledged on Tuesday to allow the Red Cross to expand its humanitarian operations. The United Nations has said that more than 235,000 Syrian refugees have registered in Iraq, Jordan, Lebanon and Turkey, while about 1.2 million people have been displaced within Syria.

"The most pressing needs are water and sanitation, shelter, essential items such as blankets and hygiene kits, as well as emergency medial assistance," Ban said.

Turkey has repeatedly urged the United Nations to protect displaced Syrians inside their country, but creating a buffer zone for displaced Syrians would be difficult because a Security Council resolution would be needed to set up a no-fly zone, and Russia and China would not approve such a move, diplomats said.

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  • Syrian Regime

    Despite major defections and a July 18. explosion in Damascus that killed four top generals, including President Bashar Assad's brother-in-law, the regime's inner circle is still powerful and united against the opposition. Assad's inner circle includes his younger brother, Maher, who commands the forces in charge of protecting the capital. It also includes the heads of the four intelligence agencies playing a major role in the crackdown. Although regime forces lost parts of the northern city of Aleppo, Syria's largest, government troops still control most cities, while the opposition dominates large parts of the countryside. <em>Caption: This June 13, 2000, file photo shows Syrian President Bashar Assad, right, his brother Maher, center, and brother-in-law Major General Assef Shawkat, left. (AP Photo, File)</em>

  • Free Syrian Army

    The main rebel fighting force for more than a year, the Free Syrian Army includes lightly-armed volunteer militiamen and defectors from Assad's military. Its overall strength and structure is unclear, but tens of thousands are believed be loyal to the group. The rebels have control over some northern areas, allowing movement of fighters and supplies from Turkey and Lebanon. Anti-Assad forces have failed to maintain any strategic footholds in big cities, being driven back from key neighborhoods in Homs earlier this year and now apparently losing ground in the largest urban center, Aleppo. The battles also suggest only weak direction from central commanders - including Turkey-based Free Syrian Army leader Riad al-Asaad. <em>Caption: In this citizen journalism image provided by Shaam News Network SNN, taken on Sunday, Aug. 12, 2012, Free Syrian Army soldiers pose for a photograph, in Sarmada, Idlib province, northern Syria. (AP Photo/Shaam News Network, SNN)</em>

  • Syrian National Council

    Based in Istanbul, the SNC has emerged as the main political opposition to Assad and has pushed for international recognition as the legitimate representative of the uprising, despite rifts with other Syrian factions. The group also has been hit by internal feuds that have led some senior members to quit. The current leader, Abdelbaset Sieda, is a Swedish-based activist for Syria's minority Kurdish community. The SNC has gained support from many countries in the West and Arab world, but it has not galvanized international backing, and critics complain its senior leadership is made up mostly of exiles out of touch with their homeland. <em>Caption: The members of the Syrian National Council and its head Abdulbaset Sieda, center, arrive for a meeting with Turkey's Foreign Minister Ahmet Davutoglu in Ankara, Turkey, Monday, July 23, 2012.(AP Photo/Burhan Ozbilici)</em>

  • The National Coordination Committee for Democratic Change

    A rival to the SNC, the National Coordination Committee is led by opposition figures inside Syria, many of them former political prisoners. SNC members accuse the group of being far too lenient and willing to engage in dialogue with the regime. In turn, the National Coordination Committee accuses the SNC of being a front for Western powers and willing to open the door to the Muslim Brotherhood and other conservative Islamist factions. <em>Caption: Member of the National Coordination Committee for Democratic Change, Morhaf Mickael speaks during a meeting of Syrian opposition parties in Brussels on Sunday, June 24, 2012. (AP Photo/Virginia Mayo)</em>

  • International Alliances

    On Assad's side are traditional Shiite allies Iran and Lebanon's Hezbollah. <em>Caption: In this photo released by the Syrian official news agency SANA, Iran's Supreme National Security Council, Saeed Jalili, meets with Syrian President Bashar Assad in Damascus, Syria, Tuesday, Aug. 7, 2012. (AP Photo/SANA)</em>

  • International Alliances

    The regime also has important political cover from Russia and China, which have used their Security Council vetoes to prevent U.N. sanctions on Syria. <em>Caption: In this Jan. 25, 2005 file photo, Syrian President Bashar Assad, left, and Russian President Vladimir Putin shake hands during a signing ceremony in the Kremlin, Moscow. (AP Photo/Sergei Chirikov)</em>

  • International Alliances

    The rebels have built an array of regional support that includes the wealthy Gulf states - led by Iran rival Saudi Arabia - and neighboring Turkey, which offers key supply routes. The West also backs the rebel forces, but has so far opposed mobilizing international military support similar to the NATO-led airstrikes that helped topple Moammar Gadhafi's regime in Libya. <em>Caption: From left, Bahrain's Foreign Minister, Sheik Khalid bin AhmedI bin Mohammed al-Khalifa, Saudi Arabia's Foreign Minister Prince Saud al-Faisal, his Turkish counterpart Ahmet Davutoglu and United Arab Emirates' Sheikh Abdullah bin Zayed al-Nahayan seenduring a group photo during the Gulf Cooperation Council (GCC) Foreign ministers meeting in Istanbul, Turkey, Saturday, Jan. 28, 2012 (AP Photo)</em>

  • Foreign Fighters

    Syria has drawn foreign fighters just as other recent conflicts such as Iraq and Afghanistan. No credible count on them exists, but anecdotal evidence suggests foreigners are coming to fight Assad. Rebel commanders downplay the presence of foreign fighters, saying their cause is a purely Syrian uprising. Mohammed Idilbi, a Syrian activist based in Turkey, says foreign ranks include Libyans, Yemenis, Tunisians and Lebanese. On Saturday, Syria's official SANA news agency claimed four Libyans were among rebels killed in Aleppo. <em>Caption: In this Sept. 18, 2011 file photo, former rebel fighters celebrate as smoke rises from Bani Walid, Libya, at the northern gate of the town. (AP Photo/Alexandre Meneghini, File)</em>

  • Extremists

    U.S. officials and others worry that Syria could become a new foothold for insurgents inspired by al-Qaida. Assessing the degree of radical Islamic ideology in the civil war is impossible, but at least one group, the al-Nusra Front, has emerged and declared allegiance to the Free Syrian Army. Al-Nusra, or Victory, has claimed responsibility for several high profile attacks, including a double suicide bombing in March that killed 27 people in Damascus and the execution-style killing of a Syrian television presenter who was abducted in July. On Friday, U.S. intelligence officials said al-Qaida has advanced beyond isolated pockets in Syria and now is building a network of well-organized cells that could include several hundred militants. <em>Caption: This photo shows Al-Qaida's new leader Ayman al-Zawahiri in a still image from a web posting by al-Qaida's media arm, as-Sahab, Wednesday July 27, 2011. Al-Qaida's new leader has lauded protesters in Syria for seeking to topple the regime of President Bashar Assad. (AP Photo/IntelCenter) </em>