Washington - The United States is considering selling Nigeria ground attack planes to help fight Boko Haram rebels, officials said on Friday, despite concerns over the local military's human rights record.Nigeria's Western allies have vowed to assist the West African giant in its fight against the brutal Islamist group, but have been cautious of providing arms to troops regularly accused of extrajudicial killings.Washington is now, however, contemplating selling Nigeria a dozen A-29 Super Tucano ground attack planes of the type US contractors have supplied to Afghanistan to help it strike Taliban guerrillas.US officials would not publicly confirm the plan, as it has not been formally approved or explained to Congress, but said Washington is looking for ways to help President Muhammadu Buhari's government.Washington has longstanding concerns about Nigeria's rights record and the government is prevented by law, under a 1997 amendment authored by Senator Patrick Leahy, from arming units that act with impunity."We are committed to implementing the letter and spirit of the Leahy Law, and will not provide assistance to any unit for which there is credible information of a gross violation of human rights," a senior administration official told AFP."We provide training and other assistance to numerous Nigerian security force units not implicated in human rights violations and we believe that assistance has and will have a significant impact on Nigeria's fight to defeat Boko Haram."Buhari, a former military dictator, was elected to the Nigerian presidency last year, replacing the incumbent Goodluck Jonathan, whose government was widely derided as incompetent and corrupt.Since Buhari came to office, the United States has sought new ways to help out in the struggle against Boko Haram, but has proceeded cautiously because of the Nigerian military's reputation for brutality."As a matter of policy, we do not comment on proposed US defense sales or transfers until they have been formally notified to Congress," said David McKeeby, spokesman for the State Department's bureau of political-military affairs."Nigeria is a strategic partner of the United States and we continue to work closely together on security matters," he said."We provide a range of assistance to Nigerian authorities, including advisors, intelligence, training, survivor support services and advice on strategic communications."Boko Haram's insurgency began in northeast Nigeria and has spread to parts of neighboring Niger, Chad and Cameroon -- where French and US forces have been more active in helping local armies fight the rebels.More than 20,000 people have been killed since fighting began in 2009, many of them in large-scale slaughters of civilians by insurgents, but some in heavy-handed military operations.