The former al-Qaeda leader believed to have been behind the Algerian hostage attack has reportedly been killed.
Mokhtar Belmokhtar was killed by Chadian soliders in Mali, Reuters reported.
Foreign Secretary William Hague said Belmokhtar's death would be "a blow for terrorism" but added that he could "not absolutely confirm" the reports.
Chadian state television announced the death of the Islamist militant, who is said to have ordered January's deadly assault on an Algerian gas plant.
The French military, which is leading the offensive in northern Mali, said it could not confirm the information.
One-eyed Belmokhtar is known as "Mr Marlboro" because of his links to cigarette smuggling in the region.
Army Chief of Staff Gen. Zakaria Ngobongue read a statement saying Chadian soldiers on Saturday had destroyed a jihadist base in the Adrar and Ifoghas mountains of North Mali, killing Belmoktar.
The purported death of Belmokhtar comes a day after Chad's president said their troops killed Abou Zeid, the other main al-Qaida commander in the region.
Speaking on the BBC's Andrew Marr show, Hague said: "These are reports from Chadian soldiers who have been fighting in northern Mali.
"We can't absolutely confirm this at the moment, and I stress that, but it would be a blow to terrorism."