US strike kills Islamic State leader in Libya: Pentagon

An F-15 fighter jet strike killed the head of the Islamic State (IS) group in Libya, the Pentagon said on Saturday, in another high-profile US hit following the targeting of the most-wanted "Jihadi John".

The announcement comes as the militant group said it was responsible for Friday's attacks in Paris that killed at least 129 people during an onslaught of bombings and shootings on the French capital, though the Pentagon said the two events were not connected.

Washington has orchestrated an air campaign going after the IS group and senior figures in Syria and Iraq, but this is the first US strike against an IS leader in Libya.

Abu Nabil, also known as Wissam Najm Abd Zayd al-Zubaydi, was the senior IS leader in Libya and may also have been the spokesman in a grisly video showing the execution of Coptic Christians, Pentagon spokesman Peter Cook said in a statement.

Cook described Abu Nabil as an Iraqi national and Al-Qaeda operative.

The footage released by IS online earlier this year showed handcuffed hostages wearing orange jumpsuits being beheaded by black-suited captors in a coastal area the group said was in the Libyan province of Tripoli.

"Nabil's death will degrade ISIL's ability to meet the group's objectives in Libya, including recruiting new ISIL members, establishing bases in Libya, and planning external attacks on the United States," Cook said, using an alternative term to refer to the Islamic State group.

"While not the first US strike against terrorists in Libya, this is the first US strike against an ISIL leader in Libya and it demonstrates we will go after ISIL leaders wherever they operate."

The Pentagon spokesman said the operation overnight against Abu Nabil was "authorised and initiated prior to the terrorist attack in Paris".

On Thursday, US President Barack Obama Obama told ABC's George Stephanopoulos that the US strategy against IS has contained the group, but been unable to “decapitate” its leadership thus far.

"I don't think they're gaining strength," he said.

"What is true, from the start our goal has been first to contain and we have contained them," Obama added. "They have not gained ground in Iraq and in Syria. They'll come in. They'll leave. But you don't see this systemic march by ISIL across the terrain. What we have not yet been able to do is to completely decapitate their command and control structures. We've made some progress in trying to reduce the flow of foreign fighters."

Oil-rich Libya descended into chaos after the fall of Muammar Gaddafi in its 2011 revolution.

IS fighters have killed more civilians than other warring factions in the North African country, but all sides are committing "large-scale crimes," International Criminal Court chief prosecutor Fatou Bensouda has said.

Saturday's US announcement came two days after the US military conducted a strike targeting the IS executioner known as "Jihadi John". 

The US has said it is "reasonably certain" that the militant was killed in a drone strike in Syria. 

Mohammed Emwazi, whose masked figure appeared in a string of graphic videos showing the beheading of Western hostages, was targeted in a combined British-US operation in Raqa, the de facto IS capital in war-torn Syria.