President Muhammadu Buhari has described the attack on the Ozubulu Church worshippers in Anambra, as the most heinous crime.
Garba Shehu, presidential spokesman, in a statement issued on Wednesday, said the president also sent a letter of condolence to the governor.
On Sunday, a gunman opened fire on worshippers at the church, killing 13 people.
The police said the attack was the fallout of a gang war between two members of the community who live abroad.
Buhari had earlier called Willie Obiano, governor of the state, to commiserate with him over the incident.
“To attack and kill defenseless people while worshipping is the most heinous of all crimes. The nation is one at deploring this monstrous crime,” the president’s letter read.
“Please, convey to the families and friends of those killed, my condolences for this utterly dastardly crime.
“Please, also convey my considerations and sympathies to the people of Ekwusigo local government area for this tragic attack.”