Suspected insurgents attacked a border town in northeastern Nigeria's Borno state and seized weapons from a military barracks as the soldiers there fled, residents and security sources said on Friday.

The incident occurred in the town of Banki in Bama district.

Insurgents in the area have upped their attacks this year against civilians and security forces.

An internal security memo from the Civilian Joint Task Force, a paramilitary unit that helps the military tackle Islamist fighters, showed the attack started at about 2130 GMT on Thursday and ended in the early hours of Friday.

"The insurgents overran the town and entered the military barracks, seizing ammunition and weapons. The commanding officer and soldiers reportedly abandoned their positions, fleeing towards Cameroon and leaving civilians behind," read the memo seen by Reuters.

One soldier from 152 Battalion, stationed in the town, said the insurgents came in large numbers, forcing security forces to retreat after heavy gunfire.

The Nigerian Army did not respond to a request for comment.

Boko Haram fighters occupied Banki a decade ago and the town is one of a number in northeast Nigeria that has repeatedly been attacked by the group as well as by Islamic State West Africa Province fighters, leading to a humanitarian crisis there.

Nigeria's military says it has counterinsurgency operations in recent months in Borno state to try to dismantle such networks in the region.

Aliyu Haruna, a Banki resident, said on Friday he had seen at least seven dead bodies in the town, including those of three soldiers. Reuters could not independently confirm the number of fatalities.

"Both military and paramilitary personnel fled to Cameroon, and it was only this morning that they returned," Haruna told Reuters by phone.