This undated image posted on a militant website on Tuesday, Jan. 14, 2014 shows fighters from the al-Qaida linked Islamic State of Iraq and the Levant (ISIL) marching in Raqqa, Syria. Two weeks of fighting between an al-Qaida-linked group and other rebel forces in Syria has killed more than 1,000 people, an activist group said Thursday, as clashes raged between the rival factions in a northwestern town. The fighting pitting the al-Qaida-linked Islamic State of Iraq and the Levant and other groups are the most serious among rebel forces since the Syrian conflict began in March 2011. (AP Photo/militant website)

BEIRUT - The United Nations on Sunday invited Iran to attend an international meeting of foreign ministers in the Swiss city of Montreux ahead of the first direct peace talks between the warring Syrian sides in the nearly three-year conflict.

But it was not clear how Syria's main Western-backed opposition group, the Syrian National Coalition, would react to the invitation to Iran. he Coalition, under huge pressure from its Western and Arab supporters, had agreed late Saturday to attend the Geneva peace talks.

U.N. Secretary-General Ban Ki-Moon told reporters at U.N. headquarters that he had issued the invitation to Iran after lengthy talks in recent days with Iranian Foreign Minister Javid Zarif.

Ban said that Zarif had assured him that Iran "understands that the basis of the talks" is the full implementation of the road map adopted by the U.S., Russia and other major powers in Geneva in June 2012. That plan called for the creation of a transitional Syrian government with full executive powers.

"Foreign Minister Zarif and I agree that the goal of the negotiations is to establish, by mutual consent, a transitional governing body with full executive powers," Ban said. "It was on that basis that Foreign Minister Zarif pledged that Iran would play a positive and constructive role in Montreux."

The U.S. State Department said it viewed Ban's invitation to Iran "as conditioned on Iran's explicit and public support for the full implementation of the (June 2012) Geneva communique including the establishment of a transitional governing body.".

"If Iran does not fully and publicly accept the Geneva communique, the invitation must be rescinded," State Department spokeswoman Jen Psaki said in a statement.

The Montreux meeting precedes peace talks scheduled to begin Friday between Syrian President Bashar Assad's delegation and Syrian opposition groups at the U.N. European headquarters in Geneva. The meeting will be moderated by the U.N.-Arab League special envoy to Syria, Lakhdar Brahimi.

Invitations to the one-day meeting of foreign ministers at a Montreux hotel had been subject to approval by the initiating states, Russia and the United States, but the two countries had been at an impasse over whether Iran, Assad's strongest ally, should attend. Invitations have now gone out to about 40 countries.

In Syria, the head of an al-Qaida-linked group in Syria reached out to rival rebel groups who have been engaged in a bloody battle with his fighters this month, calling for the two sides to end their infighting and instead unite against the government and its allies.

Rebel-on-rebel infighting between the extremist Islamic State of Iraq and the Levant and an array or ultraconservative and more moderate rebel factions has killed more than 1,000 people across opposition-held northern Syria since it began in early January. The clashes are the most serious among the opponents of President Bashar Assad in Syria's nearly three-year civil war.

In a new 16-minute audio message posted online Sunday, Islamic State leader Abu Bakr al-Baghdadi accused the other rebel brigades of stabbing his group in the back, and said the infighting only benefits the government.

"You know that we did not want this war, we did not go for it and we did not plan for it. It is clear that the beneficiaries of this war are the Nusayris and the Shiites," he said, using a derogatory term for Assad's Alawite sect, an offshoot of Shiite Islam.

But he also called for reconciliation, saying the Islamic State "is extending its hand so that we refrain from attacking each other and so that we can join forces" against Assad and his allies.

The message's authenticity could not be independently confirmed, but the audio was posted on a website commonly used by Islamic militants.

In Istanbul, meanwhile, the leadership of the Syrian National Coalition was meeting to decide on its delegation for peace talks set to open Wednesday in Switzerland.

Senior Coalition member Ahmad Ramadan said the meeting will decide who will negotiate with the Syrian government delegation at the so-called Geneva 2 conference.

Under immense pressure from its foreign patrons, the Coalition decided late Saturday to take part in the peace talks, paving the way for the first direct negotiations between the rival sides.

The U.S. and Russia have been trying to convene the Geneva conference since May, but it was repeatedly postponed. Both sides finally agreed to sit together at the negotiating table after dropping some of their conditions.

Ramadan said the 15-member delegation will include two representatives of the country's ethnic Kurdish minority, two for the rebels and two for opposition groups based in Syria.

Mustafa Osso, a member of the National Kurdish Council, said they might have two people selected to represent them.

The opposition does not want President Bashar Assad to have any role during the transitional period. Syrian government officials say Assad will not hand over power and has the right to run for president again later this year.

In Damascus, a few dozen people, including some in need of medical treatment, left the besieged rebel-held Palestinian refugee camp of Yarmouk Sunday, said a member of Palestinian Struggle Front who goes with the name Abu Jamal. The move came a day after some 200 food parcels were sent into the Yarmouk camp.

The blockade on Yarmouk has devastated the camp, where residents and activists say 46 people have died since October of starvation, illnesses exacerbated by hunger or because they couldn't obtain medical aid.

Footage aired by Lebanon's private Al-Mayadeen television station showed mostly women and children leaving the camp in ambulances.

An elderly woman, who said she suffered from diabetes, high blood pressure and an ulcer, told the station "we were suffering from hunger, cold and darkness."

"May God help the residents of the camp," the woman said.

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Associated Press writers Sameer N. Yacoub in Baghdad, and Albert Aji in Damascus, Syria, contributed to this report.

News from © The Associated Press, 2014