ISTANBUL (Reuters) - Syrian opposition talks aimed at presenting a coherent front at an international peace conference to end the civil war faced the prospect of collapse after President Bashar al-Assad's foes failed to cut an internal deal, opposition sources said on Friday.
The failure of the Syrian National Coalition to alter its Islamist-dominated membership as demanded by its international backers and replace a leadership undermined by power struggles is playing into the hands of Assad, whose forces are attacking a key town as his ally Russia said he would send representatives to the conference, coalition insiders said.
After two days of meetings in Istanbul, senior coalition players were in discussions late into the night after veteran liberal opposition figure Michel Kilo rejected a deal by Syrian businessman Mustafa al-Sabbagh, who is the coalition's secretary-general, to admit some members of Kilo's bloc to the coalition, the sources said.
Kilo has said that his group wants significant representation in the opposition coalition before it will join.
"There is a last-minute attempt to revive a kitchen-room deal. The coalition risks undermining itself to the point that its backers may have to look quickly for an alternative with enough credibility on the ground to go to Geneva," a senior opposition source at the talks said.
While the opposition remained wracked by differences, a major assault by Assad's forces and their Lebanese Hezbollah allies on a Sunni town held by rebels near the border with Lebanon over the past week was shaping into a pivotal battle.
The intervention of Shi'ite Hezbollah is justifying fears that a war that has killed 80,000 people would cross borders at the heart of the Middle East.
"It is ironic that Lebanon's civil strife is playing itself out in Syria. The opposition remains without coherence and the regime is intent on taking back anything it promises with violence," said one diplomat.
The diplomat was referring to a deepening sectarian divide between Shi'ites and Sunni Muslims in Lebanon, where Syrian troops were present for 29 years, including for most of the civil war that ended in 1990.
Assad belongs to Syria's minority Alawite sect, an offshoot of Shi'ism that has controlled Syria since the 1960s.
He has vowed to defeat what he calls terrorists and foreign agents behind the uprising, which began with months of peaceful protests and evolved into an armed revolt after months of military repression.
Washington and Moscow have been compelled to revive diplomacy by developments in recent months, which include the rise of al Qaeda-linked fighters among rebels and reports of atrocities and accusations that chemical weapons are being used.
The United States, which suspects Assad's forces of using the banned weapons, is also concerned they could eventually fall into the hands of jihadists now fighting Assad.
U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov will meet privately in Paris on Monday to discuss their efforts to bring Syria's warring parties together, U.S. and Russian officials said.
Russia said the Syrian government had agreed in principle to attend the planned peace conference, which could take part in Geneva in the coming weeks.
Senior opposition figures said the coalition was likely to attend the conference, but doubted it would produce any immediate deal for Assad to leave power - their central demand.
"We are faced with a situation where everyone thinks there will be a marriage when the bride is refusing. The regime has to show a minimum of will that it is ready to stop the bloodshed," said Haitham al-Maleh, an elder statesman of the coalition.
There was more heavy fighting on Friday in Qusair, a town controlling access to the coast that Assad's forces and Hezbollah allies have tried to take in a battle that could prove an important test of Assad's ability to withstand the revolt.
Assad wants to secure the coastal region, which is the homeland of his Alawite minority sect. He is backed by Shi'ite Iran and Hezbollah against mainly Sunni rebels supported by Saudi Arabia and Qatar.
COALITION STRUGGLES TO AGREE
Much to the frustration of its backers, the coalition has struggled to agree on a leader since the resignation in March of respected cleric Moaz Alkhatib, who had floated two initiatives for Assad to leave power peacefully.
Alkhatib's latest proposal - a 16-point plan that sees Assad handing power to his deputy or prime minister and then going abroad with 500 members of his entourage - won little support in Istanbul, highlighting the obstacles to wider negotiations.
"He has the right to submit papers to the meeting like any other member, but his paper is heading directly to the dustbin of history. It is a repeat of his previous initiative, which went nowhere," a senior coalition official said.
Washington threatened on Wednesday to increase support for the rebels if Assad refused to discuss a political end to the violence, a sentiment echoed on Friday by British Foreign Secretary William Hague, who has been pressing the European Union to amend a weapons embargo to allow arming the rebels.
Concerned by the rising influence of Islamists in the rebel ranks, Washington has pressured the opposition coalition to resolve its divisions and to expand to include more liberals.
"The international community is walking a little faster than the opposition. It wants to see a complete list of participants from the Syrian side for Geneva and this means that the coalition has to sort its affairs," a European diplomat said.
(Additional reporting by Oliver Holmes in Beirut, Thomas Grove and Alissa de Carbonnel in Moscow, Arshad Mohammed in Amman, Crispian Balmer in Jerusalem; Editing by Nick Tattersall, Peter Graff and Peter Cooney)