The United States has carried out air strikes on positions of so-called Islamic State in Libya, following a request by the United Nations-backed government there, the Pentagon says.
The strikes targeted positions in the port city of Sirte, an IS stronghold.
Libyan PM Fayez al-Sarraj, in a televised address, said the strikes caused “heavy losses”.
Western powers have become increasingly concerned at Islamic State’s growing presence in Libya, BBC said.
The air strikes are the first such US military intervention co-ordinated with the Libyan unity government.
The Pentagon said the strikes, authorised by President Barack Obama, were in support of government forces currently fighting IS militants.
The government began an offensive against IS fighters in May and said two weeks ago that it had made its largest gains to date.
Western officials say the number of IS militants in Libya, previously estimated at 6,000, is declining in the face of concerted government action and pressure from other militia.
“These actions and those we have taken previously will help deny ISIS a safe haven in Libya from which it could attack the United States and our allies,” the Pentagon statement continued, using another term for IS.
Mr Sarraj said no US ground forces would be deployed.
Libya has become increasingly divided since the fall of Muammar Gaddafi in 2011, with competing governments and rival militias seeking to gain territory and influence.
The chaos had left Libya vulnerable to an influx of IS fighters, many from Syria.