At least eight Nigerian Shia Muslims and one police officer have been killed in clashes with police at a religious procession in Kano city, police say.
Many marchers and five police officers were also injured, Police Commissioner Rabiu Yusuf said.
The group behind the procession, the Iran-backed Islamic Movement of Nigeria (IMN), has a history of tension with the security forces.
Last December troops killed 349 of its members during a crackdown.
The cause of the latest violence, which took place on the outskirts of Kano, is disputed.
Police officials said Shia procession participants attacked police with weapons including machetes and bows and arrows and seized a police rifle, which was later recovered.
Witnesses say the police fired live ammunition and tear gas into a crowd of hundreds of Shia members in an attempt to stop the march.
The sect says many of its members were killed but this has not been independently verified.
The Islamic movement was marking this year's "Arbaeen" - an annual religious event during which its members trek for many miles from various towns to Zaria - their spiritual headquarters.
The IMN has abandoned the seven-day procession and told followers to return home, the organisation told the BBC.
The IMN is Nigeria's biggest Shia organisation and has its headquarters in Zaria. It has been outlawed in Kaduna state for carrying out unlawful processions.
Its followers have been involved in a series of clashes with the security forces as well as attacks by Sunni militants.
In October, 10 IMN members were reported to have been killed in northern Katsina state following clashes with security forces during a religious celebration.
In August, a judicial review said Nigerian troops should be prosecuted for the killings in Zaria last December. IMN leader Sheikh Ibraheem Zakzaky was shot and then detained during the crackdown and remains in custody.
And last year's Shia procession from Kano to Zaria saw more than 20 people killed in an attack by a suicide bomber from the Boko Haram Sunni Islamist militant group.
Security forces were ordered to stay away from last year's procession following deadly clashes in previous years.
Shia in Nigeria
- Shia are minority in Nigeria but their numbers are increasing
- The IMN, formed in the 1980s, is the main Shia group led by Sheikh Ibraheem Zakzaky
- They operate their own schools and hospitals in some northern states
- They have a history of clashes with the security forces
- The IMN is backed by Shia-dominated Iran and its members often go there to study
- Sunni jihadist group Boko Haram condemns Shias as heretics who should be killed