By Stephanie Nebehay

GENEVA (Reuters) – Senior U.S. and Russian officials held talks on Wednesday aimed at agreeing on how to separate al Qaeda-linked militants from rebel fighters in the besieged Syrian city of Aleppo so as to pave the way for a ceasefire.

U.S. special envoy for Syria Michael Ratney led Washington’s delegation, while Moscow sent military experts whose names were not released.

They were joined by officials from regional powers such as Saudi Arabia and Qatar, but not Syria’s ally Iran which was not invited, a Western diplomat said. The Syrian warring sides themselves were not at the table.

“The idea is to engage the Russians in a discussion on the issue,” the Western diplomat said before the meeting held at the U.N. European headquarters in Geneva.

The talks follow a meeting between the United States and its allies on Tuesday that aimed to coordinate efforts toward a new ceasefire, after Russia unexpectedly announced it had halted air strikes on Aleppo.

Russia favors a U.N. proposal to evacuate jihadist fighters belonging to the Jabhat Fateh al-Sham group from the besieged zone of eastern Aleppo in return for a ceasefire.

Russia has said a planned eight-hour ceasefire on Thursday will be extended if other rebels clearly distance themselves from the group, but it will not prolong the pause unilaterally.

The last ceasefire fell apart in September, since when Russia and Syria have undertaken a massive bombing campaign on eastern Aleppo, in which hospitals have been destroyed and hundreds of civilians killed.

Britain has triggered a special session of the U.N. Human Rights Council to be held on Friday. A draft resolution seen by Reuters calls for an independent special inquiry which would name those responsible for breaking international law, including possible crimes against humanity.

Syrian President Bashar al-Assad argues that his forces have a constitutional duty to protect the civilian population and rid the city of “terrorists”.

The task of separating “moderate” rebels from Jabhat Fateh al-Sham, which was formerly known as the Nusra Front and is designated as a terrorist organization by the U.N., is complicated because they have long fought side-by-side and there is little agreement on the number of Fateh al-Sham fighters in the city.

The U.N. says there are up to 900 Jabhat Fateh al-Sham fighters out of 8,000 rebels in eastern Aleppo in total, but diplomatic sources have told Reuters there are far fewer, probably a maximum of 200.

“They are calling the shots in Aleppo,” one aid official told Reuters.

(Reporting by Stephanie Nebehay, editing by Tom Miles and Dominic Evans)