A series of bomb and gun attacks in the north-eastern Nigerian town of Damaturu has killed at least 63 people, the Red Cross says.
Witnesses said the bombs hit several targets, including churches and the headquarters of the Yobe state police.
Many people are reported to have fled the town after a night of violence.
The Islamist militant group Boko Haram told a newspaper it was behind the attack and that it planned to hit further government targets.
President Goodluck Jonathan was "greatly disturbed" by the attack, and said his government was working hard to bring those "determined to derail peace and stability in the country to book", according to a spokesman.
A series of attacks on security forces in the nearby city of Maiduguri recently have also been blamed on Boko Haram.
Nigerian Red Cross official Ibrahim Bulama, in Damaturu, told the BBC at least 63 people had been killed there.
He said two other people had been killed in attacks elsewhere. News agencies said the nearby town of Potiskum had also been attacked.
The BBC's Jonah Fisher, in Nigeria's commercial capital, Lagos, says this attack appears to be Boko Haram's bloodiest strike to date.
People visiting morgues have reported seeing 92 bodies, says our correspondent.
An unnamed local government official in Damaturu was quoted by AFP news agency as saying that hundreds of wounded people were being treated in hospital.
Witnesses said the attacks began on Friday at about 18:30 (17:30 GMT) and lasted for about 90 minutes.
Gunmen then engaged in running battles with security forces.'Church torched'
A Roman Catholic parish priest told our correspondent his church had been burnt down and eight other churches also attacked.
He described gangs of young men roaming the streets throwing improvised bombs into the churches.
The attacks followed a triple suicide bomb attack on a military headquarters in Maiduguri, in neighbouring Borno state.
Military officials said the three attackers had died.
Boko Haram, which means "Western education is forbidden", has launched frequent attacks on the police and government officials.
A known spokesman for the group contacted called Nigeria's Daily Trust newspaper to claim responsibility for the attacks on Maiduguri and Damaturu.
"We will continue attacking federal government formations until security forces stop their excesses on our members and vulnerable civilians," he said.