An army officer and self-defense commander say Boko Haram insurgents have ambushed a convoy of new recruits in northeast Nigeria, killing seven troops and abducting a female soldier.

Thursday evening's ambush occurred near Mafa town on the main road 50 kilometers (30 miles) east of Maiduguri. The northeastern city is the birthplace of Boko Haram and headquarters of the Nigerian military's campaign to crush the seven-year insurgency that has killed more than 20,000 people.

A humanitarian worker said he heard military radio traffic confirming the attack. All three spoke on condition of anonymity because they are not authorized to speak to reporters. Military spokesmen did not immediately comment.

Nigeria's military last year drove Boko Haram out of towns and forest strongholds, but isolated attacks and suicide bombings continue.