A US air strike on a jihadist training camp in Libya killed dozens of people Friday, probably including a senior Islamic State group operative behind attacks in Tunisia, officials said.

It was the second US air raid in the violence-wracked North African country targeting the fast-expanding jihadist group in the past three months.

The strike early Friday against an IS camp near the city of Sabratha "likely killed" IS operative Noureddine Chouchane, a US official said.

A jihadist safe house was destroyed in the dawn raid about 70 kilometres (42 miles) west of Tripoli, according to Hussein al-Dawadi, an official in Sabratha near the border with Tunisia.

"The raid killed 41 people who were all inside the house," Dawadi told AFP. "The vast majority of those killed were Tunisians who were probably members of IS."

A suspect wounded in the strike said he had been taken to the camp blindfolded to train in combat, Dawadi added.

The website of the Sabratha Municipal Council said rifles, rocket-propelled grenades and other weapons were found in the house, which was rented by foreigners including Tunisians.

It posted pictures that showed mattresses and blankets among the rubble and a piece of metal with the inscription "Islamic State".

Chouchane is suspected of being behind an attack in July on a beach resort near the Tunisian city of Sousse that killed 38 tourists -- including 30 Britons.

He is also accused of involvement in an attack on the National Bardo Museum in Tunis in March that killed 21 tourists and a policeman.

Both assaults were claimed by IS, which Washington is also targeting with air strikes in Syria and Iraq where the group has proclaimed an Islamic "caliphate" and committed widespread atrocities.

 'Experienced facilitator'

 Pentagon press secretary Peter Cook said the United States was still assessing the results of Friday's raid, but noted that Chouchane's death would be a significant blow to IS in Libya.

"Destruction of the camp and Chouchane's removal will eliminate an experienced facilitator and is expected to have an immediate impact on ISIL's ability to facilitate its activities in Libya, including recruiting new ISIL members, establishing bases in Libya, and potentially planning external attacks on US interests in the region," Cook said in a statement.

He added that the strike showed the United States will target the IS group "whenever it is necessary". 

In November, a US air strike in Libya killed an IS leader, Abu Nabil, an Iraqi also known as Wissam Najm Abd Zayd al-Zubaydi.

It was the first US strike against an IS leader in Libya, where the Pentagon estimates the jihadist group has about 5,000 fighters.

US President Barack Obama vowed Tuesday not to let IS build a base in Libya.

"We are working with our other coalition partners to make sure that, as we see opportunities to prevent ISIS from digging in in Libya, we take them," Obama said.

"We will continue to take actions where we got a clear operation and a clear target in mind."

In December, the Pentagon acknowledged that a group of US special operations troops who had travelled to Libya to "foster relationships" was kicked out of the conflict-torn country soon after arriving.

IS has exploited the turmoil in Libya since the overthrow of dictator Moamer Kadhafi five years ago, raising fears that it is establishing a new stronghold on Europe's doorstep.

Last June, IS fighters captured the city of Sirte, 280 miles (450 kilometres) east of Tripoli. They have since attacked coastal oil facilities and staged a string of suicide bombings.

The internationally recognised government has been based in the country's far east, having fled a militia alliance including Islamists that overran the capital in August 2014.

The alliance has its own administration and parliament in the capital. The United Nations is pushing the two sides to back a unity government to tackle jihadists and people-smugglers.