Explosions in Nigeria's central region killed 32 people on Christmas Eve and six people died in attacks on two churches in the northeast of Africa's most populous nation, officials said on Saturday.
On Friday night, a series of bombs were detonated during Christmas Eve celebrations in villages near the central city of Jos, killing at least 32 people while 74 were in a critical condition, the state police commissioner said.
Nigeria's army chief said the blasts were not part of religious clashes which flare up sporadically as tensions bubble under the surface in a country where the population is split roughly equally between Muslims and Christians.
"It (Jos explosions) was caused by a series of bomb blasts. That is terrorism, it's a very unfortunate incident," Azubuike Ihejirika said in the southern city of Port Harcourt.
The attacks come at a difficult time for President Goodluck Jonathan, who is in running a controversial campaign ahead of the ruling party's primaries on Jan. 13.
A ruling party pact says that power within the People's Democratic Party (PDP) should rotate between the mostly Muslim north and largely Christian south every two terms.
Jonathan is a southerner who inherited office when President Umaru Yar'Adua, a northerner, died during his first term this year and some northern factions in the ruling party are opposed to his candidacy.
Jonathan faces a challenge from former Vice President Atiku Abubakar for the ruling party nomination, and some fear any unrest in Africa's most populous nation will be exploited by rivals during campaigning.
"What happened (in Jos) was not religious it was political ... the aim of the masterminds is to pit Christians against Muslims and start another round of violence," the governor of Plateau state said.
In a separate incident, at least six people were killed in what appeared to be religiously motivated attacks on two churches in the northeastern city of Maiduguri.
Attackers threw petrol bombs late on Friday at a church in the city, killing five people, including a Baptist pastor. A security guard at a nearby church died in a similar assault.
"This is a worrisome situation and the government will do all it can to fish out the perpetrators of this evil act," the governor of Borno State, Ali Sheriff, said on Saturday.
"We must ensure that adequate security is provided for all citizens to worship freely without fear of molestation."
Hundreds of people died in religious and ethnic clashes at the start of the year in the "Middle Belt", the central region where the mostly-Muslim north meets the predomnantly Christian south.
There have been localised outbreaks of violence since then.
The tension is rooted in decades of resentment between indigenous groups, mostly Christian or animist, who are vying for control of fertile farmlands and for economic and political power with migrants and settlers from the north.