Abuja: Nigerian troops on Monday fought Boko Haram militants after coming under attack in a pre-dawn raid, a security source said, as they prepared for a major offensive to reclaim territory.
Scores of Boko Haram fighters stormed the town of Bama as the soldiers readied for a counter-attack on the town of Gwoza, which was seized by the extremists and later declared part of an Islamic caliphate.
Bama is 50 kilometres (30 miles) from the Borno state capital, Maiduguri.
The city is the radicals' spiritual home but they were chased out when a state of emergency was declared in May last year.
Boko Haram has seized a number of towns and villages in southern Borno and near the border with Cameroon, leading to fears that its aim is to make Maiduguri the centre of a hardline state.
"Troops have been battling Boko Haram fighters since 4 am (0300 GMT) in Bama as a result of an assault by the terrorists," a senior security source said on condition of anonymity.
"It is obviously a pre-emptive attack on troops that are deploying in Bama in preparation for a large-scale offensive to retake areas under the control of the terrorists."
The fighting forced hundreds of residents to flee to Maiduguri, said one local man, Ibrahim Maigoro. "Virtually everybody in the town has fled," he added.
"They (Boko Haram) came in large numbers in trucks and vans and attacked soldiers who responded and the intense fighting forced us to leave our homes," he added.
Boko Haram has taken over at least three major towns in Borno and at least one each in neighbouring Adamawa and Yobe states.