The attack took place 2:30 p.m. local time, Hua Jiang of the U.N. Support Mission in Libya told U.N. Radio. Among those in the convoy was Ian Martin, head of the U.N. special mission in Libya.
"Luckily nobody was hurt but [Martin] cut short his visit and has returned to Tripoli," Jiang said.
It wasn't known who was responsible for the attack, she said.
"The matter now is handled by the local authorities. As far as we understand, an investigation has been launched," she said.