Al-Qaeda's top commander in Mali has been killed, Chadian President Idriss Deby Itno said Friday, in what would be one of the most significant blows to the rebels in the seven-week French-led intervention against Islamist insurgents.

Several newspapers in Abou Zeid's native Algeria had reported his death and Washington had described the reports as "very credible".

Deby said Abou Zeid, the Mali-based operative in Al Qaeda in the Islamic Maghreb (AQIM), was killed in deadly fighting between Chadian troops and Islamist fighters on February 22.

"On February 22, we lost several soldiers in the Ifogha mountains after destroying the jihadists' base. This was the first time there was a direct confrontation with the jihadists," he said.

"Our soldiers killed two jihadist chiefs including Abou Zeid," said Deby, whose elite forces are among the best desert troops on the continent and have played a key role in the offensive to liberate northern Mali.

Algeria's independent Ennahar TV reported earlier this week that Abou Zeid was killed in northern Mali along with 40 other Islamist militants.

In Washington, a US official speaking on condition of anonymity said reports of his death seemed "very credible" and that if Abou Zeid was indeed slain "it would be a significant blow to Al-Qaeda in the Islamic Maghreb."

French officials have so far reacted with caution, with President Francois Hollande saying Friday: "Reports are circulating, it is not up to me to confirm them."

The killing of Abou Zeid, a ruthless militant linked with kidnappings and executions of Westerners, would be a major success for French forces, who intervened in Mali in mid-January to help oust Islamist rebels then in control of the north.

Algeria's El Khabar newspaper reported Friday that authorities there had carried out DNA tests to try to confirm Abou Zeid's death.

"The security services are comparing DNA taken from two close relatives of Abou Zeid with samples taken from the remains of a body supplied by French forces", it said.

French and west African troops have been hunting down rebels they dislodged from northern Mali's main cities following a lightning advance against the Islamists.

Abou Zeid, 46, whose real name is Mohamed Ghedir, was often seen in the cities of Timbuktu and Gao after the Islamists took control of northern Mali last year and sparked fears the region could become a haven for extremists.

An Algerian born near the border with Libya, Abou Zeid was a former smuggler who embraced radical Islam in the 1990s and became one of AQIM's key leaders.

He was suspected of being behind a series of brutal kidnappings in several countries, including of British national Edwin Dyer, who was abducted in Niger and executed in 2009, and of 78-year-old French aid worker Michel Germaneau, who was executed in 2010.

Abou Zeid was believed to be holding a number of Western hostages, including four French citizens kidnapped in Niger in 2010.

He was thought to have about 200 seasoned fighters under his command, mainly Algerians, Mauritanians and Malians, who were well-equipped and highly mobile.

An Algiers court last year sentenced Abou Zeid in absentia to life in prison for having formed an international armed group involved in the kidnapping of foreigners. Five other members of his family were jailed for 10 years each.

He was seen as a true religious fanatic and more uncompromising than some other leaders of north African armed Islamist groups, such as Mokhtar Belmokhtar, the mastermind of January's attack on an Algerian natural-gas facility that left 37 foreign hostages dead.

On the ground in Mali Friday, Malian troops arrested about 50 people near Gao on an island in the Niger river that was used as a hideout by armed Islamists, military sources told AFP.