Six ceasefire monitors, who were caught overnight in the crossfire of Syria's civil conflict, were handed back to their UN colleagues on Wednesday, May 16 by rebels fighting the forces of President Bashar al-Assad, Reuters reported.

The stranding of the observers in a gun and bomb attack at a funeral that killed at least 21 civilians underscored the relentlessness of the violence challenging a UN ceasefire that is meant to lead to a peaceful resolution to the uprising.

"We gave the six with their cars to a UN convoy near the entrance of Khan Sheikhoun. They are all safe, in good heath and on their way to Damascus," Free Syrian Army commander Abu Hassan said by satellite phone from the site of the handover.

The observers stayed overnight with rebels who said they feared an assault by government forces after the funeral attack.

A pro-government TV station said unidentified gunmen opened fire at the funeral. The rebel commander said a pro-Assad militia was responsible and that his forces had the names of at least 27 people killed.

The head of the monitoring mission, Major-General Robert Mood, confirmed the monitors were heading back to base.