The Nigerian police say they have arrested 400 Shia Muslims following several days of protests in the capital, Abuja.
The police say the members of the pro-Iran Islamic Movement in Nigeria (IMN) had 31 petrol bombs as well as other dangerous weapons.
The group is demanding the release of its leader, Ibraheem Zakzaky, who is accused of inciting violence and has been detained since 2015.
The army confirmed that soldiers shot dead three people on Monday accusing the protesters of trying to overrun a checkpoint.
The Shia group says more than 50 of its members were killed.
Human rights activists say about 300 members of the group were shot dead during a military crackdown three years ago.