US warplanes launch airstrikes on IS group

US warplanes bombed Islamic State targets in Libya on Monday, responding to the UN-backed government's request to help push the militants from their former stronghold of Sirte in what US officials described as the start of a sustained campaign against extremists in the city.

"The first airstrikes were carried out at specific locations in Sirte today causing severe losses to enemy ranks," Prime Minister Fayez Seraj said on state TV. Pentagon spokesman Peter Cook said the strikes did not have "an end point at this particular moment in time".

Forces allied with Seraj have been battling Islamic State in Sirte - the hometown of former leader Muammar Gadhafi - since May.