"This afternoon, multiple blasts rocked Biu. We can still hear soldiers trading fire with militants," town resident Ali Mando told The Anadolu Agency by phone.

"We fear people have been killed," he said. "Soldiers are engaging them now."

Biu, a town located 187km from provincial capital Maiduguri, has repeatedly come under attack by Boko Haram. 

This week, the insurgents seized Askira Uba, another town in Borno, where they torched homes and terrorized residents.

Since 2009, Nigeria has battled a fierce Boko Haram insurgency that has ravaged the country's volatile northeast and left thousands dead.

A seemingly emboldened Boko Haram recently stepped up its militant activity, seizing several areas of Nigeria's Adamawa, Borno and Yobe states, where it has declared a self-styled "Islamic caliphate.