An aid convoy ferrying humanitarian supplies to residents of the besieged city of Homs in Syria came under fire on Saturday, despite a three-day truce in the area.
UN and Syrian Red Cross workers were attacked by mortars and machine-gun fire from as-yet unidentified fighters.
Both the government and opposition accuse each other of being responsible.
Nine vehicles were trapped and one driver injured - five people including two rebel fighters are reported to have been killed in the attack.
The Syrian Red Cross said: "Although the team was shelled and fired upon, we managed to deliver 250 food parcels [and] 190 hygiene kits and chronic disease medicines."
The ceasefire was designed to bring aid to around 2,500 civilians who had chosen to stay in the old quarter of Homs.
Story continues after slideshow...
UN officials are to meet with members of the Syrian government to discuss whether it is safe to continue with mission.
So far it has had limited success with only 83 vulnerable people evacuated on Friday.
Much of the city is in ruins and reports of civilians eating weeds to survive are common - crude barrel bombs dropped by government helicopters have wreaked havoc.
The country's civil war has so far claimed around 130,000 lives and made millions homeless.