ROME– Pope Francis on Monday extended his “heartfelt condolences” to the faithful of the Diocese of Nnewi in Nigeria, where at least 11 people were killed and another 18 critically wounded when gunmen attacked a church in the country’s southeastern Anambra state.

The gunmen opened fire as Sunday Mass was being celebrated at the St. Philip Catholic Church. Police officials say they don’t yet know precisely who was responsible, but quickly excluded any link with the radical Islamic group Boko Haram.

“Deeply saddened to learn of the loss of life and injury following the violent attack in Saint Philip’s Catholic Church, Ozubulu, His Holiness Pope Francis extends heartfelt condolences to you and to all the faithful of the Diocese of Nnewi, in particular the families of the deceased and all those affected by this tragedy,” says the telegram signed by the Vatican’s Secretary of State, Italian Cardinal Pietro Parolin.

Addressed to the local  Bishop Hilary Paul Odili Okeke, Parolin also wrote that Francis “willingly invokes the divine blessings of consolation and strength.”

Many details of the attack remain unclear. On Sunday, Garba Umar, police commissioner of Anambra state, said it was one gunman who was responsible for the attack, but according to The Associated Press, a parishioner, Uche Nonoso, said there were two. He also put the death toll at 15.

Following the attack, Father Hygi Aghaulor, spokesman of the diocese, said that the event was a sign of loss of what is sacred: “What on earth would make people open fire on innocent unarmed worshipers including children and women on a Sunday morning?”

“We condemn this ungodly act in its totality; we pray Almighty God to console the families affected and assure them that our hearts are with them as we pray for the quick recovery of the wounded,” he said.

According to local news reports, he also urged the parishioners not to let this event discourage their usual practice of faith.

“It is when the forces of darkness attempt to overshadow goodness that the light of God shines even brighter than ever just as it happened on Easter Sunday,” he said. “Evil may make attempts but God and goodness will always triumph; we call on the good people to continue to pray for the deceased worshipers and their families.”

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After the attack, Nigerian President Muhammadu Buhari condemned the attack, calling it “an appalling crime against humanity and an unspeakable sacrilege.”

In a statement issued by one of his spokespersons, Malam Garba Shehu, Buhari said that “there was no justification whatsoever to target Church worshippers and kill them in cold blood.”

He said this kind of atrocity “plumbs the depth of depravity and extreme cruelty of the kind that words cannot adequately express.”

He also appealed for all Nigerians to “rise up” and speak against violence targeting religious groups and that perpetrated in the name of God.

No group has claimed responsibility for the attack, but the police say a manhunt has been launched. Speaking at a press conference on Sunday, Anambra’s police commissioner said they believe the incident was rooted in an isolated feud among members of the community, and ruled out involvement by Boko Haram.

Overall, the radical Islamic group born in the country is believed to be responsible for more than 20,000 deaths. However, the heavily Igbo southeastern part of the country has never been among its strongholds.