At least one person has been wounded after a convoy seeking to deliver aid to a besieged Syrian rebel-held town came under fire, the local Red Crescent said.
The incident occurred on Saturday as the convoy attempted to access Harasta in the Eastern Ghouta region outside Damascus, the Syrian Arab Red Crescent (SARC) said in a statement late the same day.
"The gunfire led to the injury of one of the truck drivers, who was seriously wounded and taken to hospital to undergo surgery," the statement said.
The convoy was a joint operation by SARC, the International Committee of the Red Cross (ICRC), and the United Nations, whose top official in Syria condemned the attack.
"Attacks on humanitarian aid workers violate international humanitarian law and compromise the humanitarian community's ability to provide the essential assistance to people who so desperately need it," Ali al-Za'tari said in a statement.
"The UN and its partners will return to East Harasta to complete this humanitarian mission and hopes that the humanitarian team will be given the required assurances of safety."
The ICRC said the 37-truck convoy had been trying to deliver food, medicine and daily essentials to 11,000 people in Harasta, who have received no aid for nearly eight months.
It said the shooting occurred "as the convoy approached the city at around 7:00pm local time", or 1700 GMT.
The incident meant the aid went undelivered and "renewed security guarantees are needed in order to proceed with this planned aid delivery", it added.
It was not immediately clear who was behind the shooting, which is not the first time aid convoys in Syria have been attacked.
In February, a convoy taking aid to a besieged part of the central city of Homs was looted by gunmen, who diverted the trucks to a government-held area and roughed up the drivers.
And in September 2016, a UN aid convoy en route to Aleppo city was hit in an air strike, though an investigation was unable to identify the perpetrators of the attack.
The United Nations estimates more than 600,000 people in Syria are living under siege, a tactic employed primarily by government forces, but also used by rebel fighters and the Islamic State group.
More than 320,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.