US planes have carried out airstrikes targeting Islamic State in the city of Sirte for the first time, the head of Libya's unity government says.

The aerial bombings caused heavy losses, according to Prime Minister Fayez al Sarraj, and are expected to continue in the hometown of former dictator Muammar Gaddafi.

They were launched at the request of the Government of National Accord (GNA) and were to support GNA-backed forces fighting the jihadist group in Sirte since May.

Mr al Sarraj said the strikes "allowed our forces to take control of strategic positions" and he stressed that no foreign troops would be deployed in Libya.

He also suggested US involvement would be "limited in time and will not go beyond Sirte and its suburbs".


Image: A fighter backed by Libya's unity government fires a mortar round in Sirte

President Barack Obama authorised the strikes which are "consistent with our approach to combating ISIL (IS) by working with capable and motivated local forces", said Pentagon press secretary Peter Cook.

He added: "The US stands with the international community in supporting the GNA as it strives to restore stability and security to Libya."

If IS lost control of Sirte, which it seized in June 2015, it would be a major setback to the insurgent group that has also faced a series of military defeats in Syria and Iraq.

The coastal city, near where Colonel Gaddafi died in a battle in 2011, is seen as one of IS' most important bases outside of the other two countries.

Around 280 pro-government fighters have been killed and more than 1,500 were injured in the battle, according to medical sources.

Image: Sirte is the hometown of former Libyan dictator Colonel Muammar Gaddafi

It had been thought as many as 6,000 Islamic State insurgents may have been in Libya, including some who have abandoned Syria.

But officials say their numbers in Libya have dropped in recent months and could be as low as 1,000 following the fighting on the ground.

The pro-GNA forces are mostly made up of militia groups from western Libya which were formed during the 2011 uprising that overthrew Col Gaddafi.

The Tripoli-based GNA came out of a UN-brokered power-sharing agreement struck in December, but has not yet been endorsed by Libya's elected parliament based in Benghazi in the east.