Islamic extremists are rampaging through villages in northeast Nigeria's Adamawa state, killing, burning and looting with no troops deployed to protect civilians, fleeing villagers said Wednesday.

More than 40 people have been killed in seven villages as houses and mosques have been burned down and businesses and homes looted this week, according to Emmanuel Kwache and state legislator Adamu Kamale.

"They don't spare anything: they slaughtered people like rams and they burned down our houses after looting food," Kwache said. "There's no presence of troops, some residents are hiding on top of hills, while those that could not run were abducted, particularly youths and women."

Kamale said he has appealed in vain to authorities to send troops since the attacks began on Friday. On Monday, he said, the militants moved from villages to the town of Michika.

In Maiduguri, some 200 kilometres north of Michika, people fleeing militant attacks in neighbouring Borno state say that Boko Haram fighters warned they are preparing "a big grave" for them in Maiduguri and that "there will be no mercy." Maiduguri is the biggest city in the northeast where troops repelled a daring offensive by hundreds of militants Sunday. At least 200 combatants were killed, according to residents and security forces.

"They kept saying they were chasing us so that we can all run into the big grave they are preparing for us in Maiduguri", said Aishatu Ba'malum, who fled from Monguno, a northeast town taken by the militants on Sunday.

Ba'malum, who lost her husband in the chaos of her flight, is among more than 200,000 people taking refuge in Maiduguri.

The city of two million residents appears to be surrounded. Three roads lead to areas held by Boko Haram. The militants are believed to be attacking the fourth road leading to the northern city of Kano, according to residents too scared to leave though they fear an imminent attack.

The extremists who denounce democracy are increasing attacks as Nigeria prepares for Feb. 14 elections. Some 10,000 people died in the five-year insurgency in the past year.