WASHINGTON » The United States launched multiple airstrikes against Islamic State militants in Libya today, opening a new, more persistent front against the group at the request of the United Nations-backed government, Libyan and U.S. officials said.

Fayez Serraj, the head of Libya’s U.N.-brokered presidency council, said in a televised statement that American warplanes attacked the IS bastion of Sirte on the Mediterranean in northern Libya. No U.S. ground forces will be deployed, he said.

The precision strikes, which targeted an Islamic State tank and vehicles, come amid growing concerns about the group’s increased threat to Europe and its ability to inspire attacks across the region, even though its numbers have been shrinking because of attacks from local forces and allied international troops.

“The presidency council, as the general army commander, has made a request for direct U.S. support to carry out specific airstrikes,” Serraj said. “The first strikes started today in positions in Sirte, causing major casualties.”

The strikes mark the start of a more intense American role in the fight against IS in Libya, as the U.S. steps in to assist the fragile, U.N.-backed government. They were the first strikes by the U.S. on the group in Libya since February, and they are expected to continue. But officials said they expect the air campaign will last weeks, not months.

Obama’s authorization for action in Sirte covers strikes, intelligence and surveillance, but not ground operations, according to a White House official, who wasn’t authorized to speak publicly about the strikes and requested anonymity.

Serraj said his government is joining the coalition against IS, adding, “This is the time for the international community to live up to its promises to the Libyan people.”

He also noted that the strikes will not go beyond Sirte and its surroundings. He said any other foreign intervention is not allowed without coordination.

His warning comes after several French commandos were killed fighting Islamic State militants. U.S., French, British and Italian special operations forces and military experts have been assisting Libyan troops fighting IS militants in eastern and western Libya.

Pentagon press secretary Peter Cook said President Barack Obama authorized the strikes following a recommendation from Defense Secretary Ash Carter and Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff.

Cook told reporters that U.S. Africa Command will coordinate any strikes with the Libyans and that the new air campaign will last as long as the Libyans request assistance to eliminate IS from Sirte. The U.S. is also providing airborne surveillance and intelligence. And a small team of U.S. special operations forces is in an operations center in Libya — outside of Sirte — to help coordinate the airstrikes, according to U.S. officials who were not authorized to discuss the matter publicly so spoke anonymously.

Mohammed al-Ghasri, the commander of a pro-government militia known as al-Bonyan al-Marsous, said his forces gave target coordinates of Islamic State positions to the U.S.

While there are no U.S. ground forces being used in connection with the latest strikes, Cook would not comment on whether other American special operations forces are currently in Libya. They have been routinely moving in and out of the country, meeting with Libyan groups.

U.S. officials earlier this year estimated there were as many as 6,000 Islamic State insurgents in Libya, including some who have abandoned Syria. But in recent months, officials say, their numbers in Libya have dropped and the group is weakening there under pressure from local militias and the U.N.-brokered government.

Two weeks ago, U.N. Secretary-General Ban Ki-moon said Islamic State fighters in Libya are facing the “distinct possibility” of defeat in their last stronghold.

And Dunford estimated in mid-July that there were only a few hundred militants still inside Sirte, which the group has used as a headquarters.

“I don’t think there is any doubt that the Islamic State in Libya is weaker than it was some months ago,” said Dunford, adding, “They’ve suffered significant casualties in and around the Benghazi area.”

In February, American F-15E fighter-bombers struck an Islamic State training camp in rural Libya near the Tunisian border, killing more than 40. And in November, a U.S. airstrike killed a top Islamic State leader in Libya.

Libya slid into chaos after the ouster and killing of dictator Col. Moammar Gadhafi in 2011. The power and security vacuum left the country a breeding ground for militias and militants, including the Islamic State group and al-Qaida affiliates.

Since 2014, Libya has been split between rival governments and parliaments based in the western and eastern regions, each backed by different militias and tribes. The U.N. brokered a deal in December, which tried to mend the rift by creating a presidency council and a unity government.

Libya’s pro-government militias — mainly from the western city of Misrata — have been waging an offensive against the Islamic State group in Sirte since May, but it has recently stalled.

Associated Press writers Maggie Michael in Cairo and Josh Lederman and Robert Burns in Washington contributed to this report.