The last buildings occupied by Islamic State militants in Sirte have fallen into the hands of Libyan fighters, officials said, as anti-IS fighters celebrated in the streets of the final IS stronghold in Libya.

The United States has launched multiple air strikes against Islamic State militants in Libya, opening a new, more persistent front against the group at the request of the United Nations-backed government.

Pro-Libyan government forces fighting to dislodge Islamic State from its key bastion of Sirte have found bodies of militants, handcuffed and shot in the head, inside army barracks in the city.