Air strikes on Boko Haram camps in northeast Nigeria have killed "many" insurgents, the military said Thursday of latest operation aimed at crushing the four-year Islamist uprising.

The bombardment last Sunday targeted the notorious Sambisa Forest area of Borno state, which is considered an extremist fiefdom and has become a key focus of the military's ongoing offensive.

News of the assault was slow to emerge as the mobile phone network in Borno remains switched off, part of the military strategy to hamper communication between the militants.

"Our men have identified and destroyed some camps of terrorists along the Sambisa area and the operation was a huge success," area army spokesman Mohammed Dole told journalists in Borno's capital Maiduguri.

"I cannot tell you the exact number of the terrorists killed but... many of them have been killed during the airstrike which we strongly believe was precise," he added.

A military source who requested anonymity told AFP that dozens of militants were likely to have been killed in the attack.

Sambisa area resident Bintu James, who spoke to reporters in Maiduguri, said "the airstrike started at night and raged on until Monday morning".

Nigeria's military has claimed a string of recent successes against Boko Haram in the northeast, the group's historic stronghold.

The government earlier this month extended the state of emergency in the area that was first imposed in May, giving the military added powers for six additional months to flush out or kill the rebel fighters.

Boko Haram launched its uprising against the Nigerian state in 2009 and has carried out attacks across northern and central Nigeria that have killed thousands.

There is evidence that the military offensive has succeeded in cornering the militants in remote parts of the northeast, leaving them only capable of attacking soft targets.

But hundreds of civilians have been killed in recent weeks, including scores of students.

Boko Haram has said it is fighting to create a strict in Islamic state in Nigeria's mainly Muslim north. The southern half of the country is mostly Christian.

The United States declared the insurgent group and its linked organisation Ansaru terrorist organisations on November 13.