The military vehicle hit the mine while patrolling in a three-vehicle convoy in Damboa district, Borno state, two military sources said.

"The 145 Task Force Battalion lost its commanding officer, a lieutenant colonel, and two soldiers after their vehicles stepped on an IED (improvised explosive device) buried by Boko Haram terrorists," one military officer said.

"Four soldiers sustained serious injuries," said a second officer.

The injured soldiers were evacuated by air to Maiduguri, the Borno state capital, for medical care, he said.

Both officers did not want to be named as they had not been authorised to speak to the media.

Boko Haram has in recent weeks stepped up attacks on military and civilian targets, raiding bases and villages.

The group's decade-long uprising to establish a hardline Islamic state in Nigeria's northeast has spilled into neighbouring Niger, Chad and Cameroon.

A regional military coalition is battling the radical Islamist group.

At least 27,000 people have been in killed in Nigeria alone, and some two million others from their homes.