The expected evacuation of thousands of rebels from in and around Yarmouk refugee camp in southern Damascus has been put on hold, reports say.
Safety issues and the killing of a top rebel have been blamed for the delay.
Militants and their families were due to be taken by bus to areas under the control of their respective groups, under a deal between rebels and the government.
Meanwhile, a rebel coalition says it has captured a key dam from so-called Islamic State (IS) in northern Syria.
A spokesman for the Kurdish-Arab Syrian Democratic Forces (SDF) said fighters backed by coalition air strikes had seized the Tishrin dam, about 22km north of the IS stronghold of Raqqa.
The spokesman, Col Talal Selo, said the capture of the dam would help disrupt an IS supply line across the Euphrates and isolate the group between northern Aleppo and its territory east of the river.
Earlier this month, pro-government media reported a deal between the Syrian regime, IS and the rival al-Nusra Front to allow members of both safe passage out of Yarmouk and Hajar al-Aswad to Raqqa and the northern province of Idlib.
Eighteen buses which will transport rebels and their families were reported to have arrived at the camp on Friday.
However, Lebanese Hezbollah al-Manar TV said the evacuation was held up because the convoy was due to pass through territory controlled by rebel group Jaysh al-Islam, whose leader was killed in an air strike later that day.
The UK-based monitoring group Syrian Observatory for Human Rights (SOHR) said it was paused for "logistic reasons" in order to secure the road to IS-held Raqqa in the north-east.
About 18,000 civilians have been trapped in Yarmouk by the fighting and a government siege since 2012.
IS militants took over parts of the camp earlier this year. They were pushed back by Palestinian militias and Syrian rebels after weeks of fierce fighting, and Yarmouk has since been divided into areas controlled by IS, al-Nusra Front and pro- and anti-government Palestinian militants.
Government forces maintain checkpoints around the area, preventing civilians from leaving.
Once Yarmouk is made safe, the UN will be able to get aid to the civilians there.