At least 5 worshippers were killed and 35 others injured when a suspected suicide bomber detonated an explosive inside a mosque in Maiduguri, the capital of Nigeria’s Borno state, during evening prayers, police said.

No group has claimed responsibility for Wednesday’s attack, which comes amid heightened security concerns in Nigeria’s northeast, where Islamist insurgents Boko Haram and its ISWAP faction have waged a 15-year campaign of violence targeting civilians, mosques, and markets.

The blast at the Al-Adum mosque occurred around 6 p.m. local time as congregants gathered for evening worship. Eyewitnesses described scenes of panic as victims were rushed to the University of Maiduguri Teaching Hospital and the State Specialist Hospital.

“Nobody knows what happened. It was during prayers that the bomb exploded. Allah has destined that this will happen but nobody can give details of how it happened,” said Masta Dalori, a market leader.

Borno State Governor Babagana Zulum condemned the attack, calling it “utterly condemnable, barbaric and inhumane”. In a statement, he urged heightened vigilance in places of worship and public spaces during the festive season.

“Attacking a place of worship is a desecration of its sanctity at a time when Muslim faithful are performing acts of worship,” he said, offering condolences to families of the dead and prayers for the injured.

Police confirmed the casualty figures and said bomb disposal teams had cordoned off the area. “Ongoing sweeping operations by police EOD are in progress,” said Kenneth Daso, spokesperson for Borno State Command.

He added that investigations were underway and advised residents to remain calm and vigilant.

Last August, gunmen attacked a mosque and nearby homes in northwest Katsina State killing at least 50, according to local officials and residents.