Islamist extremist group Boko Haram has killed more than 200 people in a raid on a village in north-eastern Nigeria, local newspaper Daily Trust reported.

Gunmen in armoured vehicles, pick-up trucks and on motorcycles attacked the village of Gamboru in Borno State on Monday night, but details about the attack only became public on Wednesday.

"People are still counting the dead bodies. They have counted over 200 and they have not finished yet," said Abdulrahman Terab, a federal lawmaker from Gamboru.

Among the dead were 16 policemen.

"The (gunmen) destroyed the biggest market while some long vehicles, loaded with assorted goods for export have been burnt by the attackers," said another resident, Abor Masa.

Local media also reported that the number of girls abducted by Boko Haram in northern Nigeria had risen to 11. Earlier reports had put the number at eight.

The abductions come three weeks after Boko Haram, which means "Western education is sinful," kidnapped more than 200 schoolgirls from a boarding school in Chibok, in Borno State.

Boko Haram leader Abubakar Shekau threatened Monday to sell and enslave those girls. It remains unclear how many are still in captivity, as some have escaped.

Nigerian President Goodluck Jonathan has accepted an offer of help from the United States in tracking down and fighting the terrorists, U.S. officials said.

The UN Human Rights Office warned Boko Haram that its actions may be judged as crimes against humanity, a label for severe and systematic acts of violence.