Damage seen Friday in Sabratha, Libya after an attack by U.S. planes. (Sabratha municipality t via Reuters)

A U.S. air attack killed dozens of militants in Libya on Friday, marking an escalation in the American campaign against the Islamic State as the militant group expands its reach from North Africa to Central Asia.

U.S. and regional officials said that U.S. F-15 fighter jets struck a suspected Islamic State camp on the outskirts of Sabratha, a restive city in western Libya, killing at least 40 people in an early-morning attack that targeted senior militant Noureddine Chouchane.

The Pentagon said Chouchane, suspected of overseeing attacks on Western tourists in neighboring Tunisia, was probably killed in the air raid, but officials cautioned that they had not yet reached a conclusive determination.

The strike comes as the Obama administration considers more-sustained military action against the Islamic State in Libya, seen as the group’s most potent affiliate outside Iraq and Syria. Strung out in several cells across the country, the group’s Libya branch is small but growing and has already gained a reputation for brutality and ambitious attacks.

U.S. officials, speaking on the condition of anonymity to discuss internal deliberations, said Friday’s strike did not signal the start of a continuous, large-scale campaign, similar to the one that has unfolded since 2014 in Iraq and Syria. The United States and its allies strike multiple Islamic State targets in those countries on a daily basis. Libya, they said, may witness a noticeable uptick in operations from the occasional actions of the recent past.

The United States and allied nations will seize opportunities to go after high-profile targets like Chouchane and established militant camps like the one in Sabratha, officials said.

“We’re going to continue to look at this and ways we may want to increase the tempo going forward,” a senior defense official said. “Those are discussions that are ongoing, and they will continue to be had for some time.”

For now, Western nations are focused on backing U.N. peace talks, which seek to broker a new unity government in Libya and end a long political vacuum that has provided a foothold for militant groups such as the Islamic State.

The operation adds to the widening scope of U.S. military operations against the Islamic State. In recent weeks, the United States has also launched a series of attacks on the group’s affiliate in Afghanistan.

President Obama, who has returned to military action in the Middle East reluctantly, has described the fight against the Islamic State as a long-term endeavor, one that will continue long after he steps down early next year. This week, Obama urged greater efforts to keep the Islamic State from “digging in” across Libya.

Islamic State militants in Sirte, Libya, shown in a video posted online in December. (AP)

“The strike outside Sabratha is an important first step in what will likely be a sustained but incremental campaign,” said Geoff Porter, president of North Africa Risk Consulting.

The Sabratha raid marked the second U.S. attack against an Islamic State militant in Libya. Late last year, the Pentagon claimed it killed an Iraqi militant known as Abu Nabil al-Anbari, considered to be the Islamic State leader in Libya. He was believed to be the man whose voice appeared in a February 2015 video showing the beheadings of 21 Christian workers in Libya, nearly all Copts from Egypt.

The Obama administration is under greater pressure to deal a decisive blow against the group, which looks increasingly capable of launching attacks well beyond Libya’s borders. Officials believe the Islamic State’s leadership has urged recruits to go to Libya because of increasing pressure they face in Iraq and Syria.

Pentagon press secretary Peter Cook said the death of Chouchane would have an “immediate impact” on the group’s ability to plot attacks against American interests.

Jamal Naji Zubia, the head of the foreign news media office in Tripoli, said the raid destroyed a large farmhouse where suspected militant fighters had gathered to hear a religious leader.

Zubia — who described the Friday airstrikes as an “accurate hit” — said most of the victims were Tunisian but included at least one Jordanian. Zubia’s office represents one of Libya’s two rival governments.

“They are believed to be from Daesh,” Zubia said in a telephone interview, using the Arabic acronym for the Islamic State, which is also known as ISIS and ISIL. “They had gathered at the house to hear a speech from one of their Tunisian imams.”

Hours after the attack, Sabratha’s municipal council posted images of what it said showed the aftermath: piles of concrete rubble and large craters ringed by palm trees. A statement accompanying the photos said rocket-propelled-grenade launchers and other weapons had been found under the debris, but there were no such images immediately posted. Various news reports in North Africa placed the death toll at around 4o and said it included mostly Tunisians and Algerians.

None of the reports carried any immediate word on the fate of Chouchane.

Porter said the targeted facility contained a military base and a processing center for foreign recruits, who make up an important part of the group’s ranks.

But the scale of the Islamic State presence in Sabratha is far smaller than it is in the coastal city of Sirte, now the group’s de-facto capital in Libya. There, Porter said, militants have a dozen training camps and a police force.

While a wide array of militant groups has thrived in the chaos of Libya’s post-revolution years, the Islamic State’s Libya affiliate began significant operations only in 2015. Since then it has taken over Sirte and sought to expand its influence elsewhere.

Islamic State fighters are now estimated to number between 2,000 and 5,000 in several different cells across Libya. Some of those are believed to be Libyans absorbed from other militant groups, while others are foreigners, including a large number of Tunisians.

“One can hope that 40 casualties in one strike will serve as a deterrent to Islamic State fence-sitters,” Porter said. “But at the same time, it could also motivate sympathizers to sign up.”

The growing Islamic State presence in Libya is viewed with particular urgency by leaders in Europe, which is already struggling to cope with new security threats and the large number of migrants arriving on its shores. Libya has become an important way station for migrants, and there are fears militants could use the country to reach Europe.

Officials said the British government supported Friday’s attack by allowing the U.S. jets to take off from British bases. British Defense Minister Michael Fallon said the attack “makes us all safer.”

For European leaders, the death of Chouchane, believed to have overseen two deadly attacks that killed scores of European and other tourists last year, would be a relief. In the first attack, gunmen killed 22 people at the National Bardo Museum, a popular destination for foreign travelers in the capital, Tunis. Several months later, a lone militant stormed a beach resort in the coastal city of Sousse, killing 38, many of them British nationals.

“We believe he trained the people who then went and carried out the attacks,” the senior U.S. defense official said of Chouchane.

Murphy and Ryan reported from Washington. Erin Cunningham in Cairo and Thomas Gibbons-Neff and Dan Lamothe in Washington contributed to this report.

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