Gunness said that the convoy, which was given clearance by Syrian authorities to reach Yarmouk, was forced to withdraw from entering the camp after bursts of machine gun fire erupted close to the trucks and a mortar exploded near the convoy.
While no one was injured in the firefight it was deemed unsafe for the convoy to proceed to the southern entrance of the camp which is an area of frequent armed conflict between the soldiers and opposition groups.
The Syrian authorities did not the give the UNRWA access to the government-controlled northern entrance to Yarmouk which Gunness said was likely to be more accessible and less risky.
In a statement, Gunness said, "This is an extremely disappointing setback for the residents of Yarmouk who continue to live in inhumanely wretched conditions. UNRWA remains undaunted by this frustrating failure and is already pressing Syrian authorities to support a further attempt to deliver humanitarian assistance to Yarmouk."