MINNEAPOLIS — A gunman opened fire with a rifle through the windows of a Catholic church 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 8 and 10, he said.

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

“I was shocked. I said, ‘There’s no way that could be gunfire,’” he said. “There was so much of it. It was sporadic.”

Bienemann’s daughter, Alexandra, said she attended the school from kindergarten to 8th grade, finishing in 2014. After she heard of the shooting, she said she was shaking and crying, and her boss told her to take the day off.

“It breaks my heart, makes me sick to my stomach, knowing that there are people I know who are either injured or maybe even killed,” Alexandra Bienemann said. “It doesn’t make me feel safe at all in this community that I have been in for so long.”

The school was evacuated, and students’ families later were directed to a “reunification zone” at the school. Outside, amid a heavy uniformed law enforcement presence, were uniformed children in their dark green shirts or dresses. Many were trickling out of the school with adults, giving lingering hugs and wiping away tears.

Dating to 1923, the pre-kindergarten through eighth grade school had an all-school Mass scheduled at 8:15 a.m. Wednesday morning, according to its website. Monday was the first day of school. Recent social media posts from the school show children smiling at a back-to-school event, holding up summer art projects, playing together and enjoying ice pops.

At a meeting of Democratic officials elsewhere in Minneapolis, Democratic National Committee Chair Ken Martin noted the shooting and “unknown amount of victims.”

The gunfire was the latest in a series of fatal shootings in the city in less than 24 hours. One person was killed and six others were hurt in a shooting Tuesday afternoon outside a high school in Minneapolis. Hours later, two people died in two other shootings in the city.

Wednesday’s school shooting also followed a spate of hoax calls about purported shootings on at least a dozen U.S. college campuses. The bogus warnings, sometimes featuring gunshot sounds in the background, prompted universities to issue texts to “run, hide, fight” and frightened students around the nation as the school year begins.

Associated Press writers Hannah Fingerhut in Des Moines, Iowa; Jennifer Peltz in New York; Jack Dura in Bismarck, North Dakota; and Sarah Brumfield in Cockeysville, Maryland; contributed to this report.