LAGOS, Nigeria - Police opened fire Tuesday on unarmed Shiite Muslim protesters in the northern city of Kaduna, leaving three dead, the spokesman for Shiites in Nigeria said, as activists accused soldiers of having killed hundreds of Shiites in "a massacre" in a nearby town in recent days.

Spokesman Ibrahim Musa of the Shiite Islamic Movement in Nigeria says 10 people were also wounded when police shot "peaceful protesters." They were condemning the mass killings over the weekend and early Monday in the ancient Muslim university town of Zaria, and demanding the military release their leader, Ibraheem Zakzaky.

The police spokesman in Kaduna did not respond to requests for information.

The bloodshed in Zaria was another blow to Africa's most populous nation, already beset by a six-year-old insurgency waged by Boko Haram, a violent Islamic group at odds with the Shiites and others who oppose its extremist views.

Amnesty International said in a statement late Tuesday that the shooting of members of the Shiite group in Zaria "must be urgently investigated . . . and anyone found responsible for unlawful killings must be brought to justice."

"Whilst the final death toll is unclear, there is no doubt that there has been a substantial loss of life at the hands of the military," said M.K. Ibrahim, director of Amnesty International, Nigeria.

Musa said soldiers Monday carried away about 200 bodies from around Zakzaky's home in Zaria, and hundreds more corpses are in the mortuary. Human-rights activists said perhaps as many as 1,000 have died.

The army said troops attacked sites in Zaria after 500 Shiites blocked the convoy of Nigeria's army chief and tried to kill him Saturday.

A witness said the Shiites barricaded the road with burning tires as Gen. Tukur Buratai approached and then stoned his convoy. The group denied that it blocked the road.

Military raids on Zakzaky's home and spiritual centers in two other areas in Zaria began hours later.