There has been widespread condemnation in the international community of a series of Christmas Day bomb attacks in Nigeria that killed almost 40 people.
The White House said the attacks were "senseless violence" and the UK foreign secretary called them "cowardly".
Militant Islamist group Boko Haram said it carried out the attacks.
A blast outside a church near the capital Abuja claimed 35 lives, while a policeman died in the city of Jos and four people were killed in Damaturu.
Nigerian President Goodluck Jonathan said the attacks were "an unwarranted affront on our collective safety and freedom", adding: "Nigerians must stand as one to condemn them."
The White House said initial investigation showed the attacks were "terrorist acts" and pledged to help Nigeria bring those responsible to justice.
Spokesman Jay Carney said: "We condemn this senseless violence and tragic loss of life on Christmas Day. We offer our sincere condolences to the Nigerian people and especially those who lost family and loved ones."
French President Nicolas Sarkozy expressed "solidarity in [Nigeria's] fight against terrorism", while German Foreign Minister Guido Westerwelle said: "Even on Christmas Day, the world is not spared from cowardice and the fear of terrorism."
UK Foreign Secretary William Hague said: "These are cowardly attacks on families gathered in peace and prayer to celebrate a day which symbolises harmony and goodwill towards others. I offer my condolences to the bereaved and injured."
Israel said it would send medical aid to Nigeria and that it "condemned in the strongest terms these attacks carried out on Christmas Day".
The Vatican said attacking a church was "blind hatred" seeking to "arouse and feed even more hatred and confusion".
President Jonathan, who is a Christian, said: "I want to reassure all Nigerians that the government will not relent in its determination to bring to justice all the perpetrators."
The first attack, outside St Theresa's Church in Madalla, near Abuja, killed 35 and wounded more than 50.
The church and surrounding homes were badly damaged.
Father Christopher Barde told AFP news agency the blast occurred as the Christmas morning service was ending.
"It was really terrible," he said. "Some [wounded] people ran towards me [saying] 'Father anoint me'."
Crowds grew angry over the attack and the slow response of the emergency services.
Reuters reports that thousands of youths have erected roadblocks on the road from the capital to the largely Muslim north, and are being tackled by security forces firing tear gas.
In Jos, a blast close to the Mountain of Fire and Miracles Church was followed by gunfire that left one officer dead, government spokesman Pam Ayuba told the Associated Press news agency.
Two explosive devices found in a nearby building were disarmed as military were deployed to the site.
In Damaturu, in the north-east, there were two explosions.
One was a suicide car bomb attack on a convoy of the State Security Service.
BBC correspondents say four people were killed there, including the suicide bomber.
There was also an explosion in the nearby town of Gadaka.
Damaturu and Gadaka are both in Yobe state, which has been the epicentre of violence between security forces and Boko Haram militants.
More than 60 people have died in fighting there this week.
A spokesman for Boko Haram, Abul-Qaqa, told local media it carried out the bomb attacks.
Boko Haram, which means "Western education is forbidden", wants the imposition of Sharia law.
The group carried out an August 2011 suicide attack on the UN headquarters in Abuja, in which more than 20 people were killed.
It was also responsible for a string of bomb blasts in Jos on Christmas Eve 2010.