Nigeria Police Force has said the attackers of St. Francis Xavier Catholic Church in Owo, Ondo state disguised themselves as church members.
In a statement, the Police Public Relations Officer (PPRO) Olumuyiwa Adejobi said the attackers used arms and explosives, an outcome of preliminary investigations.
It is however not clear the reason behind the massacre by the unidentified gunmen.
“The gunmen, from preliminary investigations, invaded the church with arms and materials suspected to be explosives.
“Police Investigators who were part of the First Responders deployed to the scene have recovered pellets of expended AK-47 ammunition, the statement said, as local media reports.
The Police said further investigations revealed that some of the gunmen disguised themselves as congregants, whiles others stood outside the church premises and fired gunshots into the church.
According to the police, “the assailants fled the scene using a Nissan Sunny car with Reg No. AKR 895 AG, which was snatched from the owner and escaped through Owo/Ute road. The vehicle has been recovered while the vehicle owner currently assisting the Police in its investigations,” the statement added.
The attack happened on the church premises while mass was ongoing on Sunday.
The United Nations in Nigeria said it "strongly condemns the brutal attacks on worshippers", according to a statement by the UN secretary general's spokesman on behalf of the UN's Resident Coordinator for Nigeria, Mattias Schmale, as reported by the BBC.
Mr Schmale appealed for calm and called for the attack perpetrators to be brought to justice.