Nigeria's army has captured a key Boko Haram camp, the militant group's last enclave in the vast northeastern Sambisa forest that was its stronghold, President Mohammadu Buhari said on Saturday.

Boko Haram has killed 15,000 people and displaced more than two million during its seven-year insurgency to create an Islamic state governed by a strict interpretation of sharia law in the northeast of Africa's most populous nation.

The militant group controlled an area in the northeast around the size of Belgium in early 2015 but has been pushed out of most of that territory over the last year by Nigeria's army and troops from neighbouring countries, moving to a base in the Sambisa forest, a former colonial game reserve.

“I was told by the Chief of Army Staff that the camp fell at about 1:35pm on Friday, December 23, and that the terrorists are on the run, and no longer have a place to hide,” Buhari said in an emailed statement.

Buhari said the capture of Camp Zero marked the “final crushing of Boko Haram terrorists in their last enclave in Sambisa forest”, which is in northeast Nigeria's Borno state.

It follows a large-scale offensive in the forest by the Nigerian military in the last few weeks.

Reuters was unable to independently verify whether the camp had been captured.

The military has said in the last few days that Boko Haram fighters are running away from the forest into surrounding areas and people have been told to be vigilant.