The United States launched a new round of airstrikes against Islamic State militants in Libya on Monday, Pentagon officials confirmed, opening a more persistent front against the terror group that had no specific “end point” as long as the fragile Libyan government needed U.S. help.

President Obama authorized the strikes after the United Nations-backed Libyan government made its first request for this type of aid, the Pentagon said. It marked the third round of U.S. strikes in Libya since November.

“I don’t want to predict the pace” of any future strikes, Pentagon Press Secretary Peter Cook told reporters at a news briefing. He denied the U.S. was leading from behind, describing the strikes as “providing military support for a partner on the ground.”

Fayez Serraj, the head of the U.N.-brokered presidency council, said in a televised statement that American warplanes attacked the ISIS bastion of Sirte, “causing major casualties,” adding that no U.S. ground forces were deployed. The precision strikes targeted an ISIS tank and two vehicles, officials said.