A bomb has targeted the US embassy offices in the eastern Libyan city of Benghazi, an embassy official said.
He said the improvised explosive device hit outside the gate of the offices and no one was injured.
"We have asked the Libyan government to increase its security around U.S. facilities," the official told Reuters. The main US embassy is in the capital Tripoli.
The attack is the latest on international missions and institutions in Benghazi, the coastal city 1000 km east of Tripoli where the uprising against Muammar Gaddafi began last year and where many overseas bodies station representatives.
On May 22, a rocket-propelled grenade hit the offices of the International Committee of the Red Cross in Benghazi, leaving a small hole in the side of the building but causing no casualties.
A month earlier, a bomb was thrown at a convoy carrying the head of the UN mission to Libya. That attack was the first of its kind targeting a foreign mission since last year's revolt overthrew Gaddafi.
There was no indication who was behind the embassy attack.
But with national assembly elections due to be held in less than 20 days' time, it underscores the instability in the country, where rival armed militia and tribesfolk are still jockeying for influence.
The weak central Libyan government has struggled to assert its authority on the myriad groups and failed to convince armed Libyans to hand over weapons that became widely available after arsenals were opened during the war last year.
On Tuesday, a US drone strike in Pakistan killed one of al Qaeda's most powerful figures, a Libyan citizen called Abu Yahya al-Libi.