Mokhtar Belmokhtar: US seeks to confirm Islamist's death
The US is seeking to clarify whether an air strike in Libya killed the Islamist militant who ordered a deadly attack on an Algerian gas plant in 2013.
Mokhtar Belmokhtar was killed in the eastern city of Ajdabiya, a statement from Libya's government said.
The US says Belmokhtar was targeted and the strike was successful, but it is analysing the operation's results and would give details "as appropriate".
Belmokhtar's death has been reported many times in the past.
US defence officials stopped short of confirming Belmokhtar's death.
"The actual impact of that raid is still being assessed," US Air Force Secretary Deborah Lee James said.
Pentagon spokesman Col Steve Warren said the Department of Defense was carrying out its own assessment after the raid.
Mohammed Hegazi, a Libyan military spokesman, told AP that tests would be conducted to confirm whether Belmokhtar was among the victims.
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.
About 800 people were taken hostage and 40 killed, most of them foreigners, including six Britons and three Americans.
The US has filed terror charges against him and officials said they believed he remained a threat to Western interests.
"Belmokhtar has a long history of leading terrorist activities as a member of AQIM, is the operational leader of the al-Qaeda-associated al-Murabitoun organisation in north-west Africa, and maintains his personal allegiance to al-Qaeda," said Col Warren.
Analysis: Jonathan Marcus, BBC Diplomatic Correspondent
Dead, or maybe still alive, either way the fact that the US is still hunting Mokhtar Belmokhtar illustrates the breadth and tenacity of the US counter-terrorism effort.
While the focus is now very much on combating Islamic State in Iraq and Syria, the US struggle against al-Qaeda franchises continues both in the Middle East (Libya in this case) and to a growing extent in sub-Saharan Africa too.
Belmokhtar masterminded the attack on the Amenas gas plant in Algeria in 2013 in which 40 people were killed, including three Americans.
He was targeted not in a drone strike but in an attack launched by two F-15 aircraft.
Libya looks set to be an area of renewed concern for the Americans, the instability prompted by the removal of Muammar Gaddafi in 2011 providing a rich vein of ungoverned space in which various Islamist militants, including Islamic State, are establishing a significant presence.
Libyan's internationally recognised Tobruk-based government said the strike came after consultation with the US. Their statement said it resulted in the death of the "terrorist Belmokhtar".
Libya has been in chaos since the ousting of Muammar Gaddafi in 2011, with its parliament forced to operate in the eastern port.
A rival parliament, the Islamist-dominated General National Congress, is nearly 1,000km (620 miles) to the west in Tripoli.
Rival militias have been battling to fill the power vacuum, with IS militants fighting other Islamists in the east.
- Known as "the One-Eyed", as he often wore an eye patch, also as "Mr Marlboro", as he used cigarette smuggling to finance his jihad
- Fought against Soviet forces in Afghanistan in the late 1980s
- A former leading figure in al-Qaeda in the Islamic Maghreb (AQIM), but left after falling out with its leaders
- Went on to lead the Islamist militia group al-Murabitoun, which has attacked local and international forces in Mali