Multiple blasts have hit at least three churches in the northern Nigerian state of Kaduna.A local Red Cross worker told the Associated Press that at least 12 people had been killed and 80 injured in the attacks.
Reports suggest there have been revenge attacks against Muslims in Kaduna city.
No one has yet claimed responsibility for the blasts, but Kaduna state has previously seen attacks by the radical Islamist group Boko Haram.
Last week the group attacked two church services, sparking violence which killed seven people. Hundreds have died in its previous attacks on churches.
Kaduna state authorities have imposed a 24-hour curfew as soldiers and police try to restore order.
Revenge attacks
Nigeria's National Emergency Management Agency said two of the blasts happened in the Wusasa and Sabon-Gari districts of Zaria.
Wusasa is the site of the first church to be built in northern Nigeria.
A third blast reportedly the nearby city of Kaduna, the state capital.
Uncomfirmed reports from news agency AFP say explosions have hit two further churches in the state, south of Kaduna city, brining the total number of attacks to five.
Boko Haram has previously justified attacks on churches by saying they were carried out in revenge for killings of Muslims in central Nigeria during earlier bouts of violence.
Recently, hardly a Sunday goes by without reports of churches being attacked in Nigeria, the BBC's Will Ross reports from Lagos.
Boko Haram says it wants Islamic sharia law in place across Nigeria and analysts suggest it is trying to trigger clashes between Christians and Muslims, our correspondent says.
Last weekend an archbishop in central Nigeria appealed to Christians not to retaliate when churches are attacked, he adds.