Ian Martin, U.N. special envoy to Libya, was among those traveling in a convoy when it was hit by an explosive device while traveling through Benghazi. Hua Jiang, a spokeswoman for the U.N. Support Mission in Libya said no one was hurt in the attack.
"The matter now is handled by the local authorities," she told U.N. Radio "As far as we understand, an investigation has been launched."
Tribal and political leaders in the eastern city of Benghazi declared their intention last month to form an autonomous government while leaving foreign policy, energy and military matters in the hands of the central government in Tripoli.
Libyan leader Mustafa Abdel Jalil described the declaration as a move by "some Arab nations" to begin a conspiracy against the Libyan people.
Libyan security since last year's civil war has been marred by tribal clashes. Victoria Nuland, a spokeswoman for the U.S. State Department, said Washington condemned the attack on the U.N. convoy.
"We are, again, taking this opportunity to call on all armed groups in Libya to exercise restraint, to refrain from violence, to work through their issues through dialogue," she said.
There were no immediate claims of responsibility for the attack.