The opposition Syrian National Coalition is to meet Saturday in the Turkish city of Istanbul to decide whether to take part in a long-delayed peace conference to end the 31-month conflict.

Samir Nashar, a member of the Western-backed coalition, told dpa that opposition members had discussed the conference with U.S. ambassador to Syria Robert Ford.

"We told the Americans that our participation must be based on solid guarantees including a clear plan and a kind of a roadmap for the transitional period," he added.

Coalition president Ahmed Jarba said last week in Cairo that the opposition would not attend unless there was a clear timeframe for Syrian President Bashar Assad to leave office.

The opposition is also opposed to Iran attending the conference. Iran is a main backer of al-Assad.

An opposition member, who asked not to be named, told dpa that if the coalition agreed to go to Geneva II, it would meet again on November 27 to decide on the delegation that would represent it.

The Geneva conference, sponsored by the United States and Russia, aims at bringing Syria's warring factions to the negotiating table.

No specific date has been set for the conference.