The 12 staffers left also because of attacks by demonstrators on the British and Italian embassies in Tripoli after a NATO airstrike on Saturday that Libya says killed a son and three grandchildren of leader Muammar Gaddafi.

"A crowd of people entered a U.N. compound and some vehicles were taken. All U.N. staff are safe and accounted for," Martin Nesirky, a U.N. spokesman, said. "The decision to leave the country was based on the overall security situation in Tripoli."

Stephanie Bunker, spokeswoman for the U.N. Office for the Coordination of Humanitarian Affairs, said local U.N. staff are staying in place.

The United Nations sent international staff to Tripoli only last month after OCHA chief Valerie Amos reached an agreement with the Libyan government on a humanitarian presence. These staffers would now cover Western Libya from neighboring Tunisia, the United Nations said.

The world body also has international staff in Benghazi, the principal city in the rebel-controlled eastern part of Libya. They were not affected by the decision, Bunker said.