The air strikes hit specific locations of the militant group, which sustained heavy losses, Prime Minister Faiez said in a TV address, adding that his government asked for the US operation.
Faiez further revealed the operation would be limited in time and restricted to the coastal town and its suburbs, also hometown of former Muammar Gaddafi.
The Pentagon confirmed the operation and said President Obama greenlighted the air strikes.
“GNA-aligned forces have had success in recapturing territory from ISIL (Islamic State) thus far around Sirte, and additional U.S. strikes will continue to target ISIL in Sirte in order to enable the GNA to make a decisive, strategic advance,” the Pentagon spokesman said.
GNA forces since May have launched a retake-campaign in an attempt to flash out the Islamists still holding the town. The fight have regained momentum as GNA forces made Misrata brigade engage street battle with the militant group now using snipers. Recent battle focused on the city center.
IS group is believed to have up to 6,000 fighters in the coastal city now empty of its population. IS conquered the city last year after driving out and massacring militiamen protecting the city.
The GNA has made the win over the militant group its top priority. In May international community and the U.S. accepted to allow unity government to purchase weapons to fight the terrorist group.
Western countries have thrown their support behind Serraj’s cabinet and offered to assist it when it calls for help.
The Monday intervention is the third by the U.S. airpower in Libya. In November U.S. claimed it killed an IS leader in the North African country. In February, a compound reportedly hosting an IS militants’ meeting was blown out by U.S. F16s, with dozens of militants killed, most of whom were reportedly Tunisians.