The jihadists attacked an army position overnight Thursday in Kamuya, a village in the northeastern state of Borno near the home of army chief of staff Tukur Yusuf Buratai's mother, the sources said.

"We lost six soldiers in the fight and 14 others sustained various degrees of injuries," an army officer said.

"The terrorists also suffered heavy losses," the officer added without giving figures.

A medic at the hospital in nearby Damaturu confirmed that the bodies of six soldiers were taken to the morgue on Friday.

Four military vehicles were also seized by the jihadists while two others were destroyed, said the military source who asked not to be identified because he was not authorised to speak about the incident.

Security sources initially told AFP that troops had fought off the militants in a three-hour battle during which the jihadists failed to overrun the post.

It was not known which Boko Haram faction was behind the attack, although the IS-affiliated Islamic State West Africa Province (ISWAP) is known to operate in the area.

Kamuya was hit twice by Boko Haram in December 2015, not long after Buratai, a lieutenant general, was appointed chief of army staff.

The latest attack came days after Boko Haram overran a military base in the town of Rann, near the border with Cameroon, forcing thousands of civilians to flee.

Fourteen people, including three soldiers, were said to have been killed in that attack, and aid workers said buildings used by humanitarian organisations had been burned to the ground.

The UN's humanitarian coordinator in Nigeria, Edward Kallon, said Friday that the attacks -- and others like it -- were having a "devastating impact" on civilians and the relief effort.

Around 1.8 million people are still homeless because of the insurgency, which began in 2009 and has killed more than 27,000.