BEIRUT: A senior UN official in Syria says the United Nations has put the evacuation of civilians from the blockaded city of Homs on hold until the fate of the detained men from rebel-held areas becomes clear.

Matthew Hollingworth said Friday that dozens of men and boys aged 15 to 55 who were evacuated from Homs during days-long truce between Syrian forces and rebels are still being questioned by Syrian authorities.

The government considers males between those ages to be potential combatants. They must obtain security clearance before they can be released.

Hollingworth says the UN would consider another evacuation of civilians once the detained men are processed.

Over the past week, the UN has overseen the evacuation of around 1,400 people from rebel-held parts of Homs, including around 400 men.

Meanwhile, a car bomb killed at least 18 people a town in southern Syria on Friday, the Syrian Observatory for Human Rights reported.

The bomb went off near a mosque in the town of Al-Yadouda near the border with Jordan, Rami Abdulrahman, director of the Observatory, said by phone.

Separately, an Al-Qaeda splinter group in Syria executed at least 13 people including relatives of fighters from rival rebel groups before withdrawing from a town near Aleppo, the Syrian Observatory for Human Rights said on Friday.

The London-based monitoring group said the men killed by the Islamic State of Iraq and the Levant militants included rebels who were detained by ISIL after laying down their arms. The Observatory said their bodies had been thrown into a well.

It did not say when the incident took place in Haritan, just northwest of Aleppo, one of the most contested areas in an almost three-year-old civil war.