The United States could lift a ban on shipping arms to Nigeria's military to help fight the militant Islamist group Boko Haram if Abuja improves its human rights record, visiting U.S. Congress members said on Tuesday.

The four lawmakers said Washington would provide more support for the fight against the group, which has killed thousands of people in its drive to set up an Islamic state in northeastern Nigeria, if alleged abuses are investigated and perpetrators punished.

The military has been accused of violating human rights while trying to defeat the six-year Boko Haram insurgency. In June, an Amnesty International report said more than 8,000 people died while being detained by the armed forces.

Legislation known as the Leahy amendment prohibits the United States from offering weapons or training to countries where there is credible information that authorities have committed human rights abuses.

Darrell Issa, a Republican congressman from California, said the new administration of President Muhammadu Buhari, who was inaugurated on May 29, could quickly deal with questions of past human rights abuses.

"If they do that, we will lift the Leahy amendment, no questions at all," he said. "So it is within the Nigerian government's authority and we encourage them to do so."

Buhari has said his administration would investigate allegations of abuses by the military and bring to justice anyone found guilty of wrongdoing.

Allegations of human rights abuses contributed to tensions between the United States and Buhari's predecessor Goodluck Jonathan.

Since Buhari's election, Washington has committed $5 million in new support for a multinational task force set up to fight the militants, who have also attacked Cameroon, Chad and Niger in recent months.

At least seven people were killed and about 20 others were kidnapped by suspected Boko Haram militants in an overnight raid on a village near Cameroon's northern border, a senior Cameroonian military officer said on Tuesday.

Issa said Washington would "continue to provide some of the most high level surveillance and tactical assistance" to support the fight against Boko Haram.

Last month, U.S. President Barack Obama offered strong support for Buhari after the two held talks in Washington, saying the Nigerian president had a "clear agenda" for defeating Boko Haram.