U.S. President Barack Obama has vowed to work with Libya to bring to justice the attackers who killed the U.S. ambassador to Libya, Christopher Stevens and other diplomats. He said, however, that the killings would not hurt U.S.-Libyan ties.

Obama branded the killing an "outrageous attack" and ordered increased security at U.S. diplomatic posts worldwide.

The United States is dispatching a Marine fleet anti-terrorist security team to boost security in Libya after an attack that killed the U.S. ambassador, a U.S. official told Reuters, speaking on condition of anonymity.

The ambassador to Libya and three embassy staff were killed in an attack on the Benghazi consulate and a safe house refuge, stormed by Islamist gunmen blaming America for a film they said insulted the Prophet Mohammad.

Gunmen had attacked and set fire to the U.S. consulate in the eastern city of Benghazi, the cradle of last year's uprising against Muammar Gaddafi's 42-year rule, late on Tuesday evening as another assault was mounted on the U.S. embassy in Cairo. California-born ambassador Christopher Stevens was killed in the assault, but it was not clear how or where he died. U.S. consular staff were rushed to a safe house after the initial attack.

An evacuation plane with U.S. commandos units then arrived from Tripoli to evacuate them from the house.

The attack raised questions about the future U.S. diplomatic presence in Libya, relations between Washington and Tripoli, the unstable security situation in post-Gaddafi Libya and whether more protests might erupt in the Muslim world over the film.