Intelligence reports "available to the (military) revealed that Abubakar Shekau, the most dreaded and wanted Boko Haram terrorists leader, may have died," a statement said.

"It is greatly believed that Shekau might have died between 25 July to 3 August 2013."

There was no independent confirmation of the claim, and previous reports of Shekau's death have turned out to be false.

According to the statement, Shekau was shot on June 30 during a clash with troops at a Boko Haram camp in the Sambisa forest in northeastern Nigeria and then taken across the border into Cameroon.

The army statement was contradictory, saying at one point that Shekau had been "mortally wounded" and "never recovered" after treatment received in Cameroon.

Shekau has been considered the leader of the main Islamist extremist faction of Boko Haram.

The group's insurgency has left at least 3,600 people dead since 2009, including killings by the security forces, who have been accused of major abuses.

Nigeria's military began a sweeping offensive in the northeast in May aiming to end the insurgency. It has however often exaggerated claims related to the drive.

National defence spokesman Brigadier General Chris Olukolade seemed to distance himself from the army statement when contacted by AFP, saying security forces were still seeking conclusive evidence of Shekau's death.

"We are yet to get confirmation on that," he said. "We are talking to our troops in the field."

Abdullahi Bawa Wase, a security analyst and rapporteur at the UN Department for Safety and Security, expressed doubts over the report, saying it could be a "mirage".

"They should have gone as far as locating where Shekau was buried, exhumed the body, conducted an autopsy and DNA tests to confirm that," he told AFP.

"It would be laughable to make such claims without going ahead to test its veracity."

A US embassy spokeswoman said she did not yet have any information on the claim and was not immediately able to comment.

The United States in March put a $7 million (5.3 million euros) bounty on Shekau's head.

Shekau has often sent out video messages from unknown locations. In a video message seen by AFP on August 12, a man who appeared to be Shekau insisted that he was in good health and referred to attacks in early August.

The military statement said the video was a fake.

"The recent video ... by the purported sect leader was dramatised by an imposter to hoodwink the sect members to continue with the terrorism and to deceive the undiscerning minds," the statement said.

Boko Haram has claimed to be fighting for the creation of an Islamic state in Africa's most populous nation and largest oil producer, though the group is believed to have a number of factions with varying aims.

Nigeria's 160 million population is roughly divided between a mainly Christian south and mostly Muslim north.

Shekau was seen as the second-in-command of Boko Haram at the time of a 2009 uprising put down by a brutal military assault which left some 800 people dead.

The leader at the time, Mohammed Yusuf, was captured by soldiers and handed over to police. Yusuf was later killed when police claimed he was trying to escape, though rights groups have called it a summary execution.

Police also claimed that Shekau was killed then, but he later emerged from unknown locations in video and audio recordings.

Boko Haram went underground after the 2009 assault, but returned more than a year later with a series of targeted killings.

It gradually expanded its targets with more sophisticated attacks, including suicide bombings.

A 2011 suicide attack on UN headquarters in the capital Abuja left 25 people dead, while coordinated bombings and shootings in Kano, the largest city in northern Nigeria, killed at least 185 people in January 2012.

The insurgency has moved in phases, at times targeting churches, security forces and schools.

While Christians have been specifically targeted, Muslims have often been its victims as well, including in brutal attacks on a mosque and a village in northeastern Nigeria that left 56 people dead this month.

Many analysts say poverty and underdevelopment in Nigeria's north have helped feed the insurgency.

Western diplomats have urged the government to address such issues as part of efforts to end the insurgency in Nigeria, long viewed as one of the world's most graft-ridden nations. (AFP)