Syria's fractured opposition pushed back the opening of talks in Istanbul to Saturday amid continuing differences over whether to attend peace talks with the government next week, sources said.
The talks of the opposition National Coalition had originally been due to get underway on Friday but were postponed due to problems posed by some 40 delegates, Coalition spokesman Khaled Saleh said.
These delegates had threatened to resign at the last meeting of the Coalition 10 days earlier, concerned at the "lack of transparency" in the re-election this month of Ahmad Jarba, seen as close to key rebel backer Saudi Arabia, as National Coalition leader.
After intense negotiations Friday half of the unhappy delegates decided to participate in the opposition talks, which are now set to begin formally on Saturday morning in a hotel in an Istanbul suburb, a western diplomatic source said.
The much-delayed Geneva II conference is aimed at finding a way out of almost three years of brutal conflict in Syria that has claimed the lives of 130,000 people and forced millions from their homes.
The Coalition is under intense pressure from Western and Arab allies to turn up to the talks in Switzerland next week, with media reports suggesting the United States and Britain have threatened to withdraw support if it fails to send a delegation.
More than 35 countries will gather in the Swiss cities of Montreux and Geneva from Wednesday for the talks on setting up a transitional government to lead the country, in line with a 2012 deal.
But recent government advances have put the rebels at a disadvantage in any negotiations.
Opposition forces are increasingly riven by rivalries between Al-Qaeda-linked jihadists and more mainstream Islamists, with fierce battles that monitors say have killed more than 1,000 people in two weeks alone.
At key preparatory talks with Russia in Moscow on Friday, the Syrian regime said it was ready to swap prisoners with the rebels in the first such mass exchange since the conflict began.
Meanwhile Turkey and Qatar held parallel talks in Ankara with four Syrian rebel groups involved in the fighting, including the Islamic Front, the country's biggest rebel alliance, seeking to convince them not to oppose, or even to participate in, the Geneva II talks, the western diplomatic source told AFP.
Those talks were expected to continue in the Turkish capital on Saturday.
At the Istanbul talks the Coalition reiterated the stance of the moderate opposition to the Geneva II talks.
"The Coalition want to participate in a political solution to the Syrian conflict," said Saleh.
The objective is to put in place a transition government in which Syrian President Bashar al-Assad will play no part, he added.