AN ISLAMIST militant who ordered a deadly attack on an Algerian gas plant two years ago that cost the lives of two Scots has been killed in US air strikes, according to officials.

The Libyan government has confirmed reports from the US military that weekend attacks killed Mokhtar Belmokhtar in the eastern city of Ajdabiya.

He was charged with leading the attack on a gas plant in Algeria in 2013 that killed at least 35 hostages, including seven Britons and three Americans.

The US says Belmokhtar was targeted and the strike was successful, but it is assessing the operation's results and would give details "as appropriate".

There was speculation that the strikes missed Belmokhtar and instead killed four members of a Libyan extremist group the US has linked to the attack on the US Consulate in Benghazi on September 11, 2012 in which Ambassador Chris Stevens and three other Americans were killed.

But in a statement the Libyan government said the strike came after consultation with the US. and that it "resulted in the death of the "terrorist Belmokhtar".

US officials said they are still assessing the results of Saturday's strike, but Pentagon spokesman Colonel Steve Warren said the military believes the attack was successful and hit its target.

Neither US officials nor the Libyan government provided proof of Belmokhtar's death, which has been reported many times in the past.

"I can confirm that the target of last night's counter-terrorism strike in Libya was Mokhtar Belmokhtar," Col Warren said. "Belmokhtar has a long history of leading terrorist activities as a member of (al Qaeda in the Islamic Maghreb), is the operational leader of the al Qaeda-associated al-Murabitun organisation in north-west Africa and maintains his personal allegiance to al Qaeda."

A US official said two F-15 fighter jets launched multiple 500lb bombs in the attack. Authorities said no American personnel were on the ground for the assault.

Born in Algeria, Belmokhtar was a former senior figure in al-Qaeda in the Islamic Maghreb (AQIM), but left to form his own militia.

He gained notoriety with the attack on the In Amenas gas plant in Algeria in 2013, which ended with the deaths of 40 workers and 30 militants, was set up with the help of inside information.

Carson Bilsland, 46, of Bridge of Cally, Perthshire, and Kenneth Whiteside, 59 of Glenrothes, Fife, were among seven British workers that died when the facility, partly operated by BP was stormed by al Qaeda in January this year.

It is not the first time authorities have claimed to have killed Belmokhtar, a militant believed to be in his 40s who reportedly lost his eye in combat and fought in Afghanistan. He was one of a number of Islamist fighters who have battled Algeria's government since the 1990s, later joining al Qaeda.

Intelligence officials said Belmokhtar essentially built a bridge between AQIM and the underworld, creating a system where various blends of outlaws now support each other and enrol local youth. He has been linked to terror attacks and the lucrative kidnapping of foreigners in the region.

The US filed terrorism charges in 2013 against Belmokhtar in connection with the Algeria attack. Officials have said they believe he remained a threat to US and Western interests. Belmokhtar had just split off from al Qaeda in the Islamic Maghreb to start his own franchise.

The Libyan government said in a statement that the strike targeting Belmokhtar came after consultation with the US so America could take action against a terror leader there.

One government official in Libya said an air strike in the north-eastern coastal city of Ajdabiya hit a group of Islamic militants also believed to be linked to al Qaida and that it killed five and wounded more.

He said the group that was wounded later fought the Libyan military guarding the hospital there, leading to an hours-long battle.