Mokhtar Belmokhtar
Terrorists' leader and former al-Qaida in the Islamic Maghreb (AQIM) member Mokhtar Belmokhtar (YouTube).

Mokhtar Belmokhtar, alleged mastermind behind Algeria's In Amenas gas plant siege in January, has been killed in Mali by Chad's armed forces, according to Chadian state television.

The siege at the BP joint venture, in which 37 hostages were killed, was one of the worst international hostage crises in recent years.

"Chadian armed forces operating in northern Mali destroyed a terrorist base. The toll included several terrorists, including their leader Mokhtar Belmokhtar," said a Chadian army statement.

Belmokhtar's death, if confirmed, would be a serious blow to al-Qaida, which is battling against French and African forces in Mali.

The US and the French have said that they cannot confirm Belmokhtar's death.

Belmokhtar, nicknamed "Marlboro Man" because of his involvement in cigarette smuggling, was from Algeria and has been involved in militant activity for two decades. The attack on the gas plant in Algeria was the first large-scale operation spearheaded by the one-eyed al-Qaida commander.

The news of his death came after Chad's President Idriss Deby announced the killing of the Aqim's (al-Qaida in the Islamic Maghreb) second-in-command, Abou Zeid.

"Both men have extensive knowledge of northern Mali and parts of the broader Sahel and deep social and other connections in northern Mali, and the death of both in such a short amount of time will likely have an impact on militant operations," Andrew Lebovich, a Dakar-based analyst, said.

Chad is one of seven African nations that have deployed troops to support the French-led offensive in Northern Mali.

French president Francois Hollande said the operation in Mali was in its final stages.

"Terrorist groups have taken refuge and are hiding in an especially difficult zone," he said.