US warplanes have carried out air strikes on positions of the Islamic State of Iraq and the Levant (ISIL) in the Libyan city of Sirte for the first time, the country's unity government head announced.
"The first American air strikes on precise positions of the Daesh (ISIL) organisation were carried out today, causing heavy losses ... in Sirte," Prime Minister Fayez al-Sarraj said in a televised speech on Monday.
The Pentagon said the raids were launched in response to a request from the unity government, the Government of National Authority (GNA).
Al Jazeera's Rosiland Jordan, reporting from Washington DC, said that the Libyan army made the request after facing many booby traps, mines, and roadside bombs in and around Sirte.
"ISIL made it physically very difficult to follow them as ISIL strengthens their grip on the heart of the city," she said.
"These airstrikes are a way of clearing the terrain and making it safer for Libyan troops to advance."
But the fighting will become more complicated as it moves towards the heart of the city because there are many civilians there who could become caught in the crossfire, she noted.
Speaking to reporters, Pentagon press secretary Peter Cook said.Cook said the US will continue to carry out air operations in coordination with the GNA.
"The specific targets will be precision targets," Cook said. "One of the targets struck today was a tank... the United States military will be rigorously involved in every step of the process.
"We don't have an end point [for the bombing campaign] at this particularly moment of time... we certainly hope that this something that does not require a lengthy amount of time."
The Tripoli-based GNA launched an operation in May to retake the ISIL bastion of Sirte, the hometown of slain ruler Muammar Gaddafi, which the fighters have controlled since June 2015
The fall of Sirte, 450 kilometres east of Tripoli, would be a major blow to ISIL, which has also faced a series of setbacks in Syria and Iraq.
The battle for Sirte has killed around 280 pro-government fighters and wounded more than 1,500, according to medical sources at the unity forces' command centre.
The pro-GNA forces are mostly made up of militias from western Libya established during the 2011 revolt that overthrew Qaddafi.
A militia set up to guard the country's main oil facilities has also been advancing on ISIL.
The GNA was the result of a UN-brokered power-sharing agreement struck in December, but it has yet to be endorsed by Libya's elected parliament based in the country's far east.

Upload a video to back it up. If Amerika says it's raining, it certainly means the sun is blazing, and If Amerika says the sky is blue, omo, just believe the sky has turned red or green.