The divided Syrian opposition will meet Friday in Istanbul to decide whether to join next week's landmark peace talks, as its Arab and Western allies ratchet up the pressure for it to attend.
On the eve of the National Coalition's meeting, US Secretary of State John Kerry made a powerful plea to the exiled group to decide in favour of the talks to be held in Switzerland on January 22.
"The United States ... urges a positive vote," Kerry said in a surprise statement to reporters.
"The Syrian people need to be able to determine the future of their country, their voice must be heard," he said.
The peace conference dubbed Geneva II is aimed at finding a way to install a transitional government to help chart an end to the war, in which 130,000 people have died since March 2011.
But parts of the Syrian opposition are wary of being drawn into a process they fear could result in President Bashar al-Assad clinging to power.
In November, it had demanded Assad's departure as a condition to joining talks.
A key bloc in the Coalition, the Syrian National Council, has also threatened to pull out if the General Assembly votes in favour of attending.
Equally set in their stance, the regime warned on Monday against preconditions for the talks to be held at the Swiss lakeside city of Montreux.
"Any person who seeks preconditions or mistakes their dreams for reality is leading to the failure of the Geneva conference before it even starts," Syrian state media quoted a foreign ministry source as saying.
Kerry sought to allay the opposition's fears that the talks would somehow legitimise Assad's regime and leave him in power, stressing that the opposition can veto any names put forward for the transitional governing body.
"Any names put forward for leadership of Syria's transition must, according to the terms of Geneva I ... those names must be agreed to by both the opposition and the regime," he said.
"This means that any figure that is deemed unacceptable by either side, whether President Assad or a member of the opposition cannot be a part of the future," Kerry added.
British media reported earlier this week that the United States and Britain had even threatened to cut support to the opposition if they failed to send a delegation to Switzerland.
"The US and UK are telling us you need to go to Geneva," an unnamed senior official in the Syrian National Coalition was quoted as saying by the BBC and the Guardian newspaper.
"They are making it very clear that they will not continue to support us the way they are doing now and that we will lose credibility with the international community if we do not go."
During a previous meeting over a week ago in Istanbul, the 120 delegates of the exiled opposition were unable to decide on a united front for the peace talks.
"Going by the animated discussions the last time, the meeting may go on until Saturday," a member of the Coalition said.
Meanwhile, Syria's regime-tolerated opposition said Wednesday it will boycott the peace conference, in protest at calls for it to form a single delegation with the exiled National Coalition.
"The executive bureau of the National Coordination Body for Democratic Change (NCBDC) has decided to reject participation in the Geneva conference in the conditions... it is currently being prepared in," the group said.
"The United Nations and the two sponsoring states (the United States and Russia) called on the Coalition to form a delegation that represented Syria's opposition in a balanced way, under the Coalition's umbrella," it added.
Russia denied Thursday harbouring a "hidden agenda" on Syria as it launched a fresh round of crisis diplomacy with top Syrian and Iranian diplomats ahead of the historic peace talks.
The allies' foreign ministers huddled in a mansion in Moscow to devise a joint stance that would ease the pressure on President Assad to step down when the peace talks open next week after months of delays.