The leader of the armed group Boko Haram, Abubakar Shekau, may have died of gunshot wounds some weeks after a clash with soldiers, the Nigerian military has said.

"It is greatly believed that Shekau might have died between 25 July [and] 3 August 2013", a statement issued on Monday said.

The military added that it believed Shekau was shot on June 30 during a battle with troops at a Boko Haram camp in the Sambisa forest in northeastern Nigeria - an area of major Boko Haram activity. The army claimed Shekau was then secretly taken to Cameroon for treatment, but later died.

Shekau was described in the statement as "the most dreaded and wanted" Boko Haram leader.The United States recently offered a $7m bounty for information leading to his arrest.

Though the death of Shekau would be a blow to Boko Haram's campaign, the group has several factions without one homogeneous leadership structure. Spin-off groups like Ansaru, which has claimed responsibility for kidnapping and killing Westerners, are believed to operate independently.

No evidence yet

Al Jazeera's Yvonne Ndege, reporting from Abuja, said that some observers may cast doubt on the military's claims. Our correspondent said it was difficult to get independent confirmation because the movements of rights groups and journalists are severely restricted in areas where Boko Haram operate.

"The Nigerian military have not yet provided any video or photographic evidence to back up what they're saying," she said. "The public no doubt will be waiting for some...evidence of Abubakar Shekau's death."

Past reports of Shekau's death have proved false.

Nigeria's military began a sweeping offensive in the country's northeast in May, after a state of emergency was invoked by the country's president, Goodluck Jonathan.

However, Ndege said there had been sustained attacks since then, including the killing of at least 30 people earlier this month at a mosque in Borno state, one of three states in the northeast affected by the state of emergency.

Boko Haram wants to depose the government and impose Islamic law.

At least 3,600 people have died since 2009 in fighting between the group and the army.