Nigeria's military said on Tuesday, Dec 24, it had killed at least 50 Islamist rebels fleeing towards Cameroon in a battle in which 15 of its own soldiers and five civilians also died, according to Reuters.

Nigerian forces have stepped up an offensive in the volatile northeast in the past few days, after Boko Haram fighters armed with grenade launchers and anti-aircraft guns attacked an army barracks in the town of Bama last week.

The military often reports significant casualties among insurgents, while rarely admitting losses among its own troops or civilians. The figures it gave for Monday's battle near the Cameroon border could not immediately be verified.

Defense spokesman Brigadier General Chris Olukolade said the military had targeted insurgents behind the Bama attack and that 20 vehicles used in that raid had been spotted from the air and destroyed.

"Although a good number of the insurgents escaped with bullet wounds, while some have been arrested, over 50 of them died in the course of exchange of fire with ground troops in the operations to apprehend fleeing terrorists," he said.

Boko Haram, which is fighting to revive a medieval Islamic caliphate in today's religiously-mixed Nigeria, rarely talks to the media but occasionally sends video statements anonymously.

President Goodluck Jonathan last month extended a state of emergency in areas worst affected by the insurgency.

The military began an offensive in May that initially drove the Islamists from large parts of the northeast, but they fell back into the hilly area of Gwoza, near the Cameroon border, from where they have launched deadly counter-attacks.

Boko Haram is still seen as the main security threat to Nigeria, Africa's leading energy producer.

The group claimed responsibility for a coordinated strike on December 2 on the air force base and military barracks in the main northeastern city of Maiduguri in the first major assault on the heavily guarded city this year.

Fearing Boko Haram attacks over Christmas, Nigerian police have ordered extra patrols, surveillance and covert operations to protect potential targets.