Boko Haram militants have killed at least 40 people in north-eastern Nigeria, according to witnesses, BBC News reports.

The attacks took place in the villages of Debiro Hawul and Debiro Bi in Borno state. Residents say the militants drove into the towns and began shooting, looting and burning houses.

In a separate attack, a young female suicide bomber reportedly killed at least 10 people in the neighbouring state of Yobe. A witness said the girl, who detonated explosives in the town of Gujba, was about 12 years old. The Islamist group has not commented on the attack but it is known for carrying out such bombings.

Earlier this year, the Nigerian army seized Gujba from the militant group Boko Haram.

Some 18,000 people have been killed in Nigeria since the group began a campaign of violence in 2009.

One resident who fled Debiro Hawul said that the attack had taken the village by surprise.

"It never occurred to us we would be the next target," Umaru Markus told the AFP news agency.

"The gunmen slaughtered 22 people who were not fast enough in fleeing and went about looting homes, grains silos and drug stores," he added.