Boko Haram militants seized back the border town of Marte in northeastern Nigeria and attacked outlying villages Friday, weeks after the military said it had contained the Islamic extremists in a forest stronghold, ABC News cited an official said.

Deputy Gov. Zannah Umar Mustapha of Borno state also said officials fear hundreds of female suicide bombers have slipped into the state capital, Maiduguri.

Twenty civilians were killed by the military cannon fire, according to Muhammad Gava, a spokesman for a civilian defense group that fights Boko Haram. Another 16 people died, including soldiers and civilian fighters, according to Gava.

"We were thinking that the insurgency should have subsided," Mustapha said. "Our thinking was that every other place should have been blocked so that the insurgency would be curtailed to a restricted area. But that has not been the case, because the insurgents have been fleeing to other communities."

An offensive on forest camps has freed some 700 girls and women held captive by the extremists. But it appeared to have become bogged down by land mines and booby traps set up by Boko Haram.

Thousands have died, as many as 10,000 just last year, in the nearly 5-year-old Islamic uprising and more than 1.5 million people have been driven from their homes. ."