ABUJA, Nigeria — The Nigerian Islamist group Boko Haram has used children as young as 12 as fighters and abducted and raped women, while the government has failed to account for hundreds of detained men and boys, Human Rights Watch said.

Boko Haram, which is fighting to impose Islamic law in Africa’s top oil producer, has killed hundreds of people in recent attacks, New York-based Human Rights Watch said Friday in an emailed statement.

“For a group that claims to be religious, Boko Haram’s tactics are the most profane acts we can imagine,” Daniel Bekele, Africa director at Human Rights Watch, said in the statement. “The killing and mutilation of ordinary Nigerians, the abduction and rape of women and girls, and the use of children for fighting are horrifying human rights violations.”

President Goodluck Jonathan has imposed emergency rule in three northern states where Boko Haram is most active.

The United States named the militant group on Nov. 13 a Foreign Terrorist Organization, a move analysts said would probably strengthen the resolve of the authorities in the capital, Abuja, to crack down on the insurgency.

Nigerian army spokesman Ibrahim Attahiru declined to comment on Human Rights Watch’s statement at a news conference Friday in Abuja.

INTENSIFIED ATTACKS

Witnesses told Human Rights Watch that Boko Haram intensified its attacks on civilians following the state of emergency declaration in May in Borno, Yobe, and Adamawa states, the group said.

Since the death in police custody of its leader, Mohammed Yusuf, in July 2009, Boko Haram has killed thousands of people in attacks in the mainly Muslim north and Abuja.

The security forces have detained hundreds of young men, Human Rights Watch said, citing witness accounts.

“Scores of those arrested have disappeared, and their family members, despite great efforts, have been unable to locate them,” it said.

The emergence of an anti-Islamist militia group allied with the security forces is a “worrisome” development because it prompts more retaliatory attacks on civilians, according to the statement.

“The Nigerian government should thoroughly and impartially investigate the fate of the disappeared, as well as credible allegations of arbitrary detention, use of torture, and deaths in custody by security forces,” it said.