The Islamist insurgency has devastated the region since 2009, leaving at least 20,000 dead, displacing more than 2.6 million others and triggering a wider humanitarian crisis.

Buhari, his military commanders and government have repeatedly insisted for several years that the jihadists were on the verge of defeat, despite frequent evidence to the contrary.

But his latest statement goes further as it implies a total end to hostilities.

Addressing troops in the garrison town of Monguno, some 140 kilometres (87 miles) from the Borno state capital, Maiduguri, Buhari said Boko Haram fighters were surrendering "willingly".

"It's evident that we are in a post-conflict stability phase, which has been made possible by the good work of our armed forces," he added.

Former military ruler Buhari came to power three years ago on a promise to defeat Boko Haram, which is aligned to the Islamic State group and threatens security in the Lake Chad region.

But while there have been clear military gains since a counter-insurgency was launched in early 2015, suicide bombings and raids remain a constant threat, particularly to civilians.

Last month, 43 people were killed in a wave of suicide attacks in the town of Damboa, 90 kilometres southwest of Maiduguri. Soldiers and civilians have also been killed in Niger and Chad.

The United Nations said in a progress report of its operations in Nigeria this year to May 31 that "large-scale displacements" of people were still a weekly occurrence.

"In the past seven months, since hostilities intensified in the northeast, over 130,000 people have been displaced, sometimes for the second or third time," it added.

It warned that such displacements would continue into at least next month, while aid workers have expressed concern about the government encouraging IDPs to return home.

Towns and villages damaged and destroyed by nine years of fighting lacked shelter, clean water, sanitation, health and education facilities, and security remained volatile.

Buhari, 75, is seeking re-election in February next year and aid workers said his latest statement about hostilities was likely political.

He is also under pressure from increasing insecurity elsewhere, including renewed bloodshed in a long-running farmers-herders conflict that has left some 1,000 dead since January.

"Everything points to the fact that there's still major, major problems" in northeast Nigeria, one aid worker told AFP.