Nigerian authorities suspect the Daesh terrorist group's West African arm ISWAP carried out a massacre in a Catholic church in the southwest of the country on Sunday in which 40 people were killed, Interior Minister Ogbeni Rauf Aregbesola said on Thursday.
The attack during Mass at Saint Francis' church in Owo last Sunday also injured more than 80 people and marked a rare assault in a relatively safe region.
Government officials said they suspected the ISWAP, a group that usually operates far away in the northeast of the country, was behind the violence.
"We have been able to locate the perpetrators of that sad horrendous attack. From all indications, we are zeroing-in on ISWAP. The animals in ISWAP wanting attention and recognition are suspected to have launched that attack," said Aregbesola.
"The number of deaths now is 40," Governor Arakunrin Oluwarotimi Akeredolu said in a statement Wednesday.
"Receiving treatment (in hospital) we have 61," he said, adding that 26 others have been discharged.
Children were among the dead and injured, authorities have said.
On Tuesday the governor had given a toll of 22 dead and 58 wounded.
Police said the gunmen hid among worshippers inside the church and also opened fire on the congregation through the windows from outside.
Fragments of explosives and three unexploded improvised explosive devices were found at the scene.
A priest who was conducting the service told Agence France-Presse (AFP) that some worshippers managed to hide in the vestry with others, including children, for about 20 minutes before emerging to scenes of carnage.
No group has yet claimed responsibility for the attack.
The governor said the bloodshed was "indescribable."
He added that residents were understandably angry but should not try to seek revenge.
Security has been stepped up and the state will soon issue an executive order requiring all places of worship to install CCTV, he said.
The attack drew international condemnation, including from Pope Francis.
Nigeria's military and police are battling on several fronts, with extremist groups in the northeast, criminal gangs in the northwest and center and separatist violence in the southeast, among other threats.