Deadly Nigeria bomb attacks condemned by world leaders
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."
'Solidarity'
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"; Kazinform cites BBC.
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