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 assessing the operation’s results and would give details “as appropriate”.
He was targeted not in a drone strike but an attack launched by two F-15 aircraft.
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, when about 800 people were taken hostage and 40 killed, most of them foreigners, including six Britons and three Americans.
“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 Pentagon spokesman Col Steve Warren.