Jihadist leader Mokhtar Belmokhtar "supervised" twin suicide bombings which killed at least 20 people in Niger on Thursday, the Mauritanian agency Alakhbar quoted a spokesman for his group as saying.
"It was Belmokhtar who himself supervised the operational plans of attacks," which "targeted elite French forces assuring the security of installations of the nuclear operator (Areva) and an Algerian military base," said El-Hassen Ould Khalil, spokesman for Algerian jihadist Belmokhtar's "Signataries in Blood" group.
The reported death of the jihadist known as Mr Marlboro is described as a "major breakthrough" in the battle against al Qaeda.
The al Qaeda commander who led the deadly assault on the In Amenas gas plant in Algeria has been killed, according to the Chad military.
Armed forces from Chad say Mokhtar Belmokhtar was killed when they targeted and destroyed a terrorist base in northern Mali.
The death of one of the world's most wanted jihadists would be a major blow to al Qaeda in the region and to Islamist rebels already forced to flee towns they had seized in northern Mali by an offensive by French and African troops.
"On Saturday, March 2, at noon, Chadian armed forces operating in northern Mali completely destroyed a terrorist base," Chadian armed forces spokesman General Zacharia Gobongue said in a statement read on national television.
"The toll included several dead terrorists, including their leader Mokhtar Belmokhta."
Foreign Secretary William Hague hailed the reported killing as a "blow to terrorism". He told the BBC: "It would be a blow to terrorism and to the criminal network around this man and other people."
Belmokhtar claimed responsibility for the seizure of dozens of foreign hostages at the In Amenas gas plant in Algeria in January in which more than 60 people were killed.
The report of his death comes days after Chad's President Idriss Deby said soldiers in Mali had killed another leading al Qaeda commander in the Sahara, Adelhamid Abou Zeid.
French officials said they could not confirm the killing of either Abou Zeid or Belmokhtar.
Sky's foreign affairs editor Tim Marshall said that if his death is confirmed, al Qaeda in North Africa will have been deprived of "one of the most battle-hardened leaders".
The Foreign Office says it is aware of the reports and is looking into them.
Algerian-born Belmokhtar has been fighting as an Islamist militant for more than two decades.
He claimed to have received military training in Afghanistan before returning to Algeria, where he lost an eye fighting in the Islamist insurgency in the 1990s.
He then joined AQIM - which operates across the Sahara - before breaking off to lead his own group.
He is also known as Mr Marlboro because of his alleged role in cigarette smuggling in the region.
Chad is one of several African nations that have contributed forces to a French-led military intervention in Mali aimed at ridding its vast northern desert of Islamist rebels who seized the area nearly a year ago following a coup in the capital.
Western and African countries are worried that al Qaeda could use the zone to launch international attacks and strengthen ties with African Islamist groups like al Shabaab in Somalia and Boko Haram in Nigeria.
Mokhtar Belmokhtar: Profile Of Mr Marlboro.
He was known as Mr Marlboro because of his cigarette smuggling. The French intelligence service called him "The Uncatchable".
Born in central Algeria in 1972, Mokhtar Belmokhtar grew obsessed with Jihadi ideology in his teens. At 19 he volunteered to fight alongside the mujahedeen in Afghanistan.
He missed most of the fighting there as the Soviets withdrew as he arrived but he did encounter senior members of what was to become al Qaeda - receiving training in a Jalalabad base.
In the early 1990s he returned to Algeria to join Islamic militant groups. He served them as a quartermaster - rapidly rose to dominate operations in the south of the country during the Algerian civil war.
Described by the then head of France's Territorial Surveillance Directorate (Direction de la surveillance du territoire – DST) as Algeria's link to al Qaeda, Belmokhtar maintained strong links to the movement's core in Pakistan.
But he was a vital element in the expansion of al Qaeda in the Islamic Maghreb (AQIM). A franchise of the Jihadi movement AQIM was seen as the poorly performing franchise during the last decade.
But Belmokhtar forged links with Tuareg rebels in the south Sahara from Mali to Niger and into Mauritania.
He rapidly expanded a criminal empire to fund his political and military operations from smuggling cigarettes, diamonds, drugs and people into Europe.
He further stuffed his war chest with funds from hostage taking operations. In 2003 he was implicated in the kidnapping of 32 Europeans in the Sahara.
In 2008, he took control of negotiations for the release of two Austrian hostages. And in 2009 took control of two Canadians kidnapped in Mali and released by him for allegedly £3m and
freedom for several of his associates from Malian jails.
Robert Fowler was a UN special envoy in Mali when he was kidnapped and then handed on to Belmokhtar.
He described the man who has now projected himself on to the world stage from the relative obscurity of the Saharan wastes.
"He is very cold. Very business-like. I was afraid for my life all the time. I was afraid for my life when I woke up in the morning and when I went to sleep at night. He is a very serious player," Mr Fowler told ABC News in the US.
Belmokhtar's movement got a huge boost from the collapse of the Libyan regime of Muammar Gaddafi.
The Tuareg fighters he had employed from Niger, Mali and Chad, fled his service carrying with them vast stockpiles of heavy weapons and bringing many years of combat experience.
This influx of new weapons and fighters allowed for al Qaeda-related groups to capture much of northern Mali and establish closer links between groups from Mauritania to Somalia and into the Arabian Peninsula.
Some intelligence agencies believe that Belmokhtar fell out with the AQIM leader in the north of Africa, Abdulmalek Droukel.
But al Qaeda is a franchise. Its strength lies in fragmentation. A devolved series of groups are harder to infiltrate or destroy than one large organisation.
Al Qaeda expert Aaron Zelin describes this as "controlled fragmentation".
French intelligence services had been trying to kill or capture Belmokhtar for more than a decade. They believed that he had the capacity to mobilise French citizens with their roots in North Africa for terror operations inside Europe.
After France launched its war against Islamists in Mali, many of whom are connected to Belmokhtar, his organisation which calls itself "The Masked Ones", vowed to continue attacks against western targets in Africa and beyond.
Belmokhtar's attack in Algeria meant his name was heard more widely as his movement posed a strategic threat to Europe's energy supplies.