The charges come as the guardian of Nigeria's estimated 80 million-plus Muslims, Sultan Muhammad Sa'ad Abubakar of Sokoto, warned the government against actions that could further radicalize Muslims in a country that already has lost 20,000 lives to the Boko Haram Islamic uprising.
Human Rights Watch said it doubts the Nigerian military's version that raids over three days on three Shiite locations in northern Zaria town followed an attempted assassination of the army chief.
"It is almost impossible to see how a roadblock by angry young men could justify the killings of hundreds of people. At best it was a brutal overreaction and at worst it was a planned attack on the minority Shia group," said the Africa director of Human Rights Watch, Daniel Bekele.
The New York-based group said the army's version "just doesn't stack up."
As many as 1,000 people may have been killed, rights activists say, sparking protests in Nigeria's mainly Muslim north that spread to Tehran, the Iranian capital, and New Delhi in India.
Video footage shot by sect members and posted on YouTube appears to show soldiers calmly setting up before the shootings began.
Without provocation, the soldiers fired on people coming out of the mosque, initially killing an estimated five people and injuring others, including children attending classes at the center, according to Human Rights Watch, which said it interviewed many witnesses separately at locations in Kaduna and Zaria, on December 17 and 18.
The group's leader, Iran-influenced Ibraheem Zakzaky who dresses like an ayatollah, suffered four bullet wounds, according to family doctors, and is among scores detained.
