Syria's opposition is edging towards agreeing to international peace talks in Geneva but wants approval from fighters inside the country first to give the process more legitimacy, sources at talks in Istanbul said late on Saturday.

The leadership of the Syrian National Coalition is meeting to agree its stance on the so-called "Geneva 2" talks, which aim to end Syria's two-and-a-half year civil war by creating a transitional governing body.

A draft resolution reaffirms the coalition's commitment to a political solution to the conflict and echoes a declaration in London last month by the Friends of Syria pro-opposition alliance, ruling out any role for President Bashar al-Assad in a transitional administration, opposition sources said.

The 108-member coalition is to due vote on the resolution, with 50 percent plus one vote needed for it to pass.

But opposition sources said coalition members want to seek the backing of rebel fighting units, community leaders and activists inside Syria for the resolution, to counter criticism that it is out of touch with those battling on the ground.

Major Islamist rebel brigades have declared their opposition to the Geneva process if the conference does not result in Assad's removal and some have said they would charge anyone who attended the planned international talks with treason.

"We have to share this (draft resolution) with the forces inside, as well as community leaders and activists. We need to confirm this with them," said one member of the Syrian National Council, a grouping within the coalition.

He said the resolution already contained tough conditions for participation in the conference, but those on the ground might want to tighten them further.

That could mean a delay.

Several sources said the approval could be obtained before the end of the Istanbul meeting, which could run into next week, but others said a final decision could take up to two weeks.

U.S. envoy Robert Ford met the coalition's senior leadership in Istanbul before their meeting to push them to approve the Geneva talks, coalition members said, and diplomats and other foreign officials said they were optimistic.

"We want them to come to the decision on their own and think about it properly. It has to have support of the Syrian people," one senior Western diplomat said.

The proposed peace conference is meant to build on a June 2012 agreement among world powers in Geneva that called for a transitional authority with full executive powers, but left open the question of whether Assad could play any part.

An opposition source said the draft resolution also had conditions including the release of opposition detainees, and end to air raids and to blockades on food and medicine imposed by Assad's forces on opposition areas.

Even if the coalition votes to attend the peace talks, it still has to form a broad delegation which Washington wants to include some of the coalition's rivals within the opposition.

Opposition sources say the coalition's leadership has agreed to a proposal by the Syrian Democratic Union bloc to convene a meeting on November 23 to discuss Geneva with other opposition groups, including some tolerated by the Assad government. – Reuters