Two churches in northern and central Nigeria have been attacked, one by gunmen and the other by a suicide bomber, witnesses said.
There was no immediate word on casualties and no claim of responsibility. Attacking churches has become a trademark tactic of the Islamist group Boko Haram.
In Biu Town, in north-eastern Borno state, witnesses said three gunmen started firing at people outside a church before entering the main building. "Many people have been killed and wounded," said Hamidu Wakawa, who was at the church.
In the south-western city of Jos, a man drove a car to the entrance of the Christ Chosen church and detonated a bomb, said Emmanuel Davou, 53, who lives nearby.
Christian youths set up roadblocks and had to be dispersed by police, he said. "Angry youths have gone wild, even attempting to prevent the security personnel from getting to the scene of the incident. They had to force their way out by shooting in the air to disperse them."
Police were unable to give immediate details on either attack.
Boko Haram has been blamed for hundreds of killings over the past two years. Its leader, Abubakar Shekau, frequently says attacks on Christians are revenge for killings of Muslims in Nigeria's volatile "Middle Belt", where the largely Christian south and mostly Muslim north meet and sectarian tensions run high.
The group usually targets security forces, although attacks on Christian worshippers are increasingly common. Last Sunday a suicide car bomber killed at least 12 people at a church in the remote northern town of Yelwa.