Syria's main rebel bloc, the National Coalition, is meeting in Istanbul to decide whether to attend peace talks that world powers want to hold in Geneva.
The meeting is expected to continue through Sunday.
Rebels have balked at the proposed "Geneva 2" talks, insisting they will only attend if Syrian President Bashar al-Assad resigns beforehand. But the U.N.-Arab League envoy for Syria, Lakhdar Brahimi, says there can be no preconditions.
In Istanbul Saturday, a member of the National Coalition, Haitham Al Maleh, said he is skeptical that such a Geneva conference could succeed, and he repeated that coalition members will not take part if - as he put it - the Syrian regime continues to "kill people, arrest people and burn the country."
There is no schedule for any "Geneva 2" meetings, although Western officials have expressed the hope they could begin before the end of this yeard.
Meanwhile, Syrian activists say rebels have regained control of a key base near Aleppo international airport in fierce fighting overnight that left more than 50 people dead.
The Britain-based Syrian Observatory for Human Rights said Saturday that government troops captured part of the base early on Friday. However, a night-time counterattack rebel fighters is reported to have reversed all of those losses.
The observatory said more than 30 rebels and about 20 government troops died in the fighting.