Gunmen attacked a church in Nigeria on Sunday, killing 22 people and wounding 50.

The massacre occurred late morning at St. Francis Catholic Church in Owo, approximately 200 miles northwest of Lagos.

Parishioners had gathered in the church that day to celebrate Pentecost. A survivor of the attack, John Nwovo, 35, told AP News that the priest was ending the service with a blessing when shooters opened fire around 11:30 a.m.

Several unidentified attackers, some of whom had disguised themselves as parishioners, fired AK-47s and detonated improvised explosives, killing dozens of men, women, and children.

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Nigerian President Muhammadu Buhari lambasted the killers in a statement relayed by his spokesman, “Only fiends from the nether region could have conceived and carried out such dastardly act … No matter what, this country shall never give in to evil and wicked people.”

Nigeria has suffered for years from terrorist attacks, armed insurgencies, and religious violence, but as of Tuesday, June 7, no militant group or organization had claimed responsibility for the massacre.

The country’s inspector-general of police, Usman Alkali Baba, ordered a “comprehensive” investigation into the attack, deploying special police units to hunt down the gunmen, reported ABC News.

“[The inspector-general] assures that the heartless killers of the harmless victims, particularly innocent children, would be made to face the full wrath of the law,” stated Olumuyiwa Adejobi, a spokesperson for the Nigerian police in the capital city of Abuja.

Reports of the number of dead fluctuated in recent days, with some estimates placing the death toll at over 50.

Nigerian officials revised the number to 22 confirmed dead, reported FOX News.

A doctor who helped treat the wounded at Owo’s Federal Medical Center commented on the scene.

“I have attended to a good number of casualties, but what I saw yesterday was far beyond whatever I have seen before in my life,” he said to AP News. “This calamity befell all age grades, from toddlers to the old ones.”