More than 20 people have been killed in attacks in Nigeria claimed by Islamist extremist group Boko Haram.
The fresh wave of violence targeted Christians, with gunmen opening fire on groups of mourners and church worshippers in a number of towns.
The deadliest of the attacks hit the town of Mubi in northeastern Nigeria yesterday, when five gunmen opened fire on Christian Igbos at a house as they mourned the death of a friend killed in a shooting the night before.
Various death tolls were given. Residents and a relief official reported up to 17 dead, while police said 12 were killed, with between two and five people killed the previous night in the same town.
Last night gunmen raided an area housing churches in Yola city centre, in the same state as Mubi, and killed at least eight people inside a church, according to a local journalist and a hospital source.
On Thursday evening, gunmen had stormed a church in the northeastern city of Gombe and opened fire on worshippers, killing six people including the pastor's wife.
The attacks further intensified fears that the violence could lead to wider religious clashes in Nigeria, Africa's most populous nation, which is roughly divided between a mainly Muslim north and predominantly Christian south.
A purported spokesman for Islamist group Boko Haram, blamed for scores of attacks in Nigeria, had on Sunday issued a three-day ultimatum for Christians to leave the north.
The same spokesman, Abul Qaqa, claimed responsibility for the attacks at the Mubi church and on the mourners, adding they were in response to the ultimatum.
He also said a state of emergency declared in hard-hit areas last weekend by President Goodluck Jonathan would not stop the sect.
"We are responsible for the attacks in Mubi and Gombe," Qaqa, who claims to speak on behalf of Boko Haram, told journalists in the northeastern city of Maiduguri by phone.
"We are extending our frontiers to other places to show that the declaration of a state of emergency by the Nigerian government will not deter us.... We can really go to wherever we want to go."
He called on the federal government to release all arrested Boko Haram members as a condition for attacks to stop.
"The attacks are part of our response to the ultimatum we gave to southerners to leave the north," he added.
Jonathan declared the state of emergency on 31 December in parts of four states hard hit by the attacks blamed on Boko Haram, but there has been no halt to the violence.
Yola and Mubi, located in Adamawa state near the Cameroon border, and Gombe are not part of the areas under the state of emergency decree.
Mobs also fired into the air and explosions were heard in the northeastern city of Potiskum yesterday evening, residents said.
Potiskum falls under the state of emergency decree and has previously been hit by heavy violence.
While Boko Haram has been blamed for increasingly deadly attacks for months, including an August suicide bombing of UN headquarters in Abuja that killed 25, the violence has taken on a different dimension with the recent church attacks.
A wave of Christmas bombings that killed 49 people, most of them outside of a Catholic church as services were ending, led to intense fear and outrage in Africa's largest oil producer.
There have been fears of reprisals from Christians, and Christian leaders have warned they will defend themselves if attacks against them continue.
Boko Haram is a shadowy group believed to have a number of factions with differing aims, including those with political links and a hardcore Islamist faction.
It launched an uprising in 2009 put down by a brutal military assault which left some 800 people dead.
Since the group re-emerged in 2010, it has been blamed for increasingly sophisticated and deadly attacks, including suicide bombings, but its structure and aims have become far less clear.
