Nigerian police have arrested the leader of a Muslim Shia sect and about 100 of his followers after clashes in the northern city of Sokoto.
Sokoto is the spiritual home of Nigeria's Muslims
Malam Kasimu Rimin Tawaye and his supporters were detained after police besieged the Shia headquarters.
Thursday's clashes between Shias and Sunni Muslims followed the shooting of a prominent Sunni cleric, well known for his sermons against the Shias.
One of the suspected gunmen was beaten to death during a pitched battle.
The Sunni preacher was shot on Wednesday night while travelling home by motorbike taxi after taking prayers.
The sultan of Sokoto, the spiritual head of Nigeria's Muslims, said Mallam Umaru Dan-Maishiye died after being shot in the head. He appealed for calm.
"Do not take the law into your own hands... the security agencies are investigating," Sultan Mohammadu Sa'ad Abubakar said on local radio stations.
Sokoto police spokesman Mohammed Umar Dakingari told the BBC that two suspects were being held in connection with the shooting of the cleric.
There has been regular friction between Sunnis and Shias in northern Nigeria, and civic leaders are meeting on how to calm tensions.
In April, the killing of a militant cleric in the city of Kano led to fighting between Islamist militants and the army.
But the BBC's reporter in Sokoto, Hassan Sahabi Sanyinnawal, says this is the first time that something of this nature has happened in Sokoto.