Nigeria-based Boko Haram has killed more than 1,000 civilians this year and forced hundreds of abducted girls and women to convert to Islam and marry fighters, a leading human rights group has said.

Human Rights Watch said people are desperate despite recent successes of a multinational offensive which has seized back dozens of towns from the Islamic extremists.

The New York-based group also said Nigerian security forces torched a village and killed at least five civilians.

A report based on accounts from witnesses and media said Nigeria's government was not doing enough to protect its civilians.

Nigeria is preparing for critical presidential elections on Saturday which Boko Haram is threatening to disrupt because it opposes democracy.