LAGOS, Nigeria — Dozens were believed to be dead after assailants attacked a Catholic church in southwestern Nigeria on Sunday, firing on worshipers as they celebrated Mass, according to local officials.
The attack at the St. Francis Catholic Church in Owo, in Ondo State, was the deadliest attack on a church in Nigeria in years, and brought the kind of violence usually seen in the country’s north to a relatively peaceful area of Africa’s most populous nation.
The attack occurred on Pentecost Sunday as dozens of worshipers were gathered at the church. At least four assailants stormed the building, according to the police.
It was the first time that a church had been attacked in the Ondo state in recent years, bringing a new sense of insecurity to a state that had been spared the levels of violence seen elsewhere in Nigeria.
President Muhammadu Buhari, who has promised to end Nigeria’s insecurity, condemned the attack as a “dastardly act.”
As of Sunday night, there had been no claim of responsibility and the motive for the massacre was unclear.
Most attacks on churches have been in the north, but they have become less frequent than they were at the height of the Boko Haram insurgency around 2015. In the southwest, where the church attack took place on Sunday, there have been kidnappings, most often by herdsmen seeking ransom, and there have been conflicts with herdsmen over new restrictions on open grazing.
Officials were still assessing the toll of the attack on Sunday. Videos posted on social media showed bodies lying in pools of blood between church pews.
Oluwole Ogunmolasuyi, the majority leader of Ondo’s State Assembly, went to the scene of the massacre and said he had seen at least 20 dead, including many children. He estimated the death toll at 70 to 100.
Adelegbe Timileyin, a federal lawmaker representing the Owo area, told The Associated Press that at least 50 people had been killed.
The attack came amid renewed social and economic tensions in Nigeria, where regular killings and kidnappings have compounded a deep sense of insecurity and resentment of the government ahead of the next presidential election scheduled for February.
As Mass was taking place around 11:30 a.m., armed assailants shot at worshipers from outside the church while other gunmen targeted people inside the building, the police said in a statement on Sunday evening.
“It is a black Sunday in Owo,” Ondo’s governor, Arakunrin Akeredolu, said, condemning a “vile and satanic attack” against people “who have enjoyed relative peace over the years.”
Nigeria is roughly divided between Christians living predominantly in the south and Muslims populating the country’s north.
Much of the violence plaguing Nigeria, such as killings and kidnappings, have mostly occurred in the country’s northwest and center.
Last month, gunmen killed dozens of people in the central state of Plateau, and in April eight people were killed and dozens were kidnapped on a popular train route connecting the capital, Abuja, to the regional hub of Kaduna in the north.
The attack, on a route that the authorities boasted was a safe alternative to a highway where kidnappings by bandits are commonplace, angered many Nigerians who blamed Mr. Buhari for his inability to stem the surge of violence.
No group has claimed responsibility for the train attack. The authorities have said that elements of the Boko Haram terrorist group had teamed up with local bandits for the attack. Dozens of passengers are still being held hostage by kidnappers.
Episodes of violence occasionally flare up between the country’s Muslims and Christians. Last month, a Christian student was beaten to death and her body set on fire after fellow students accused her of sending blasphemous messages about the Prophet Muhammad in a WhatsApp group conversation.
Last week, a man was killed and burned to death in Abuja after an argument with a Muslim cleric, the police said. In late May, the head of Nigeria’s Methodist Church was kidnapped and released a few days later after Methodist officials said they had paid a ransom.
On Sunday after the attack on St. Francis Catholic Church, Mr. Akeredolu, Ondo’s governor, also warned against vigilantism in response.
Ben Ezeamalu reported from Lagos, Nigeria, and Elian Peltier from Dakar, Senegal.