A gunman opened fire with a rifle through the windows of a Catholic church on Wednesday and struck a group of children celebrating Mass during the first week of school, killing two and wounding 17 in an act of violence the police chief called “absolutely incomprehensible”.

Minneapolis Police Chief Brian O’Hara said the shooter – armed with a rifle, shotgun and pistol – approached the side of the church and shot through the windows toward the children sitting in the pews during Mass at the Annunciation Catholic School.

O’Hara said the shooting suspect is dead and in his early 20s and does not have an extensive known criminal history. Officials are looking into his motive.

“This was a deliberate act of violence against innocent children and other people worshipping. The sheer cruelty and cowardice of firing into a church full of children is absolutely incomprehensible,” said the police chief, who noted that a wooden plank was placed to barricade some of the side doors.

The children who died were eight and 10, he said.

Minnesota Governor Tim Walz called the violence “horrific” in a social media post.