The US ambassador to Libya and three other Americans have been killed in an attack by gunman on the US consulate in Benghazi.

The militants attacked the compound late on Tuesday night, in protest at a film being produced in the US that many people in Libya have deemed blasphemous to the Prophet Muhammad.

Christopher Stevens, the ambassador, and the three other members of staff, were being driven to a safer location when their vehicle was hit in a rocket attack.

Libya's Deputy Prime Minister Mustafa Abu Shagour has condemned the attack.

Writing on Twitter he said the act was "cowardly".