Syria's opposition resumed talks on Saturday aimed at creating a coherent front crucial to a proposed international peace conference, struggling under Western and Arab pressure to close their fractious ranks and elect a viable leadership.
Failure of the opposition to unite could weaken the hand of conference co-sponsors Russia and the United States in ending Syria's civil war, which has killed 80,000 people and threatens to spill across borders and whip up wider sectarian conflict.
The U.S. and Russian foreign ministers are to meet privately in Paris on Monday to discuss how to coax Syrian President Bashar al-Assad and the opposition into peace talks in Geneva.
As opposition leaders deliberated, Syrian government forces reinforced by Lebanese Hezbollah fighters stepped up a fierce campaign to seize more rebel terrain in the border town of Qusair on Saturday, sources on both sides said.
Rebels are largely surrounded but fighting back hard, seeing it as a critical battle to maintain cross-border supply routes and deny Assad a victory they fear may give him the upperhand in the prospective peace talks next month.
Sources at the Syrian National Coalition, which began its third day of meetings on Saturday, said its main players had agreed to focus on international demands for a broadening of the Islamist-dominated coalition.
Attempts to strike a grand bargain involving veteran liberal campaigner Michel Kilo and businessman Mustafa al-Sabbagh, Qatar's point man in the coalition, went nowhere in talks that stretched overnight, senior coalition sources said.
"We are back to square one," one of them told Reuters.
Concerned by the rising influence of Islamists in the rebel ranks, the United States has pressed the opposition coalition to resolve its divisions and bring more liberals into the fold.
The coalition will try again to admit some members of the Kilo block into the organization, which is controlled by the powerful Muslim Brotherhood and Sabbagh faction, possibly creating a third force in the coalition.
Saudi Arabia, the most powerful Arab adversary of Assad, has agreed to play a more active role in furthering the coalition cause, diplomats and coalition members said.
CLASHING SAUDI, RUSSIAN PRIORITIES
Saudi Arabia, the sources said, will want to see the Geneva conference, which could convene in the next few weeks, put the exit of Assad at the top of the agenda.
But they said Russia, a longtime ally of Assad, wanted it to focus on a ceasefire although there is scant rapport between opposition politicians abroad and rebels inside Syria.
The inability of the 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 who, according to Russia, is prepared to send representatives to the peace conference.
"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.
Senior opposition figures said the coalition was likely to attend the conference, but doubted the meeting would yield any immediate deal for Assad to leave power - their central demand.
While the opposition remained riven by differences, the assault by Assad's forces and their Shi'ite Muslim Hezbollah allies on Qusair, a Sunni town held by rebels near Lebanon over the past week, is evolving into a pivotal battle.
Qusair controls access to Syria's Mediterranean coast, the heartland of Assad's minority Alawite community, and the battle may prove a weighty test of his ability to withstand the revolt.
Assad is backed by Shi'ite Iran and Hezbollah against the mainly Sunni rebels supported by Saudi Arabia and Qatar.
Hezbollah's intervention is hardening fears that the civil war will cross borders at the volatile 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'ite and Sunni Muslims in Lebanon, where Syrian troops were present for 29 years, including for most of the Lebanese civil war that ended in 1990.
The United States threatened on Wednesday to increase support for the rebels if Assad refused to discuss a political solution. That was echoed on Friday by British Foreign Secretary William Hague, who has been pressing the European Union to amend a weapons embargo to allow arms shipments to the insurgents.