Nigerian police have reportedly shot dead three unarmed Shiite Muslim protesters in the city of Kaduna, as activists accused soldiers of having killed up to 1,000 Shiites in a nearby town.
Ibrahim Musa, spokesman of the Shiite Islamic Movement in Nigeria, said 10 people were also wounded when police shot "peaceful protesters" in the northern city.
The protesters were condemning the mass killings over the weekend and early on Monday in the ancient Muslim university town of Zaria, and demanding the military release their leader, Ibraheem Zakzaky.
The bloodshed in Zaria was yet another blow to Africa's most populous nation, already beset by a six-year-old insurgency waged by Boko Haram, a violent Islamic extremist group which is at odds with the Shiites and others who oppose its extremist views.
Mr Musa said soldiers carried away about 200 bodies from around Mr Zakzaky's home in Zaria on Monday, and hundreds more corpses are in the mortuary.
Human rights activists said hundreds, perhaps as many as 1,000, have been killed.
The army said troops attacked sites in Zaria after 500 Shiites blocked the convoy of Nigeria's army chief, and tried to kill him on Saturday.
A report from the military police said some Shiites were crawling through tall grass towards General Tukur Buratai's vehicle "with the intent to attack the vehicle with (a) petrol bomb" while others "suddenly resorted to firing gunshots from the direction of the mosque".
Ojo Momodu, a witness, said the Shiites barricaded the road with burning tires as General Buratai approached and then stoned his convoy.
The group, however, denied that it blocked the road.
The military raids on Mr Zakzaky's home and spiritual centres in two other areas in Zaria began hours later.
Chidi Odinkalu of the Nigerian Human Rights Commission called the attacks "a massacre".
He posted photos on social media showing a bulldozer tearing apart a Shiite shrine, but doubts later emerged about whether the image was actually from Zaria. He also said Mr Zakzaky's home was destroyed.
Mr Odinkalu said Mr Zakzaky suffered four bullet wounds and one of his wives was killed in raids that began on Saturday and ended on Monday morning. He was quoting the family doctor.
Two of Mr Zakzaky's sons were also killed and one was wounded, according to Mr Musa.
Mr Odinkalu and other human rights activists said there are hundreds of bodies at the mortuary of the Ahmadu Bello University Teaching Hospital on the outskirts of Zaria.
"Citizens must ask, who ordered this carnage?" Mr Odinkalu tweeted.
Major General Adeniyi Oyebade, who was in charge of the military operation, told reporters on Monday night that the military acted because they had reports the Shiites were gathering for an attack.
"Of course, because of the report I got that they are mobilising, I had to order that the Gyallesu (Zakzaky's residence) and Huissaniya (shrine) be brought down," he said.
He said both the military and the Shiites suffered casualties and that the dead were still being counted.