A black-clad gunman killed two children and wounded 17 other people on Wednesday when he opened fire on students attending Mass at a Minneapolis Catholic school, authorities said.

The assailant, a man in his early 20s, fired dozens of rounds through the church windows and then took his own life, officials said. He was armed with a rifle, a shotgun and a pistol, they said.

“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,” Minneapolis Police Chief Brian O’Hara told reporters.

The shooting occurred two days after school started at Annunciation Catholic School, a private elementary school with about 395 students, connected to a Roman Catholic church in a residential area in the southeast part of Minnesota’s largest city.

Local TV showed parents ducking under yellow police crime tape and leading students out of the school.

Officials said the shooter did not have an extensive criminal history. They did not provide his name and said they were trying to identify a motive. Law enforcement was investigating multiple online videos to determine if they were posted by the shooter, according to two sources who spoke on condition of anonymity.

Local hospitals said they were treating 15 children and two adults, with many suffering gunshot wounds.

School shootings occur on a regular basis in the US, spurring ongoing debates about gun laws and school safety. There have been more than 140 such incidents so far this year, according to the K-12 School Shooting Database.

“Don’t just say this is about thoughts and prayers right now. These kids were literally praying. It was the first week of school. They were in a church,” Minneapolis Mayor Jacob Frey said at a news conference, visibly angry.

Earlier, police and paramedics were responding to an active shooter situation at a church, local news reported, citing the Minneapolis Police Department.

“There is no active threat to the community at this time. The shooter is contained,” the City of Minneapolis said on X.

The shooting occurred at the Annunciation Church, which is also home to a grammar school.

“The families of children at the school can go to the reunification zone at the Annunciation School,” the city said in a second post on X.

Meanwhile, Minnesota Governor Tim Walz said in a post on X that he had been briefed on the shooting and would continue to provide updates.

“I’m praying for our kids and teachers whose first week of school was marred by this horrific act of violence,” Walz said, without providing details on potential victims.

Later, United States President Donald Trump said in a post on Truth Social that he had been fully briefed on the incident and that the White House “will continue to monitor the terrible situation”.

“The FBI quickly responded and they are on the scene,” Trump added. “Please join me in praying for everyone involved!”

The confirmed shooting comes after a wave of false reports of active shooters at US college campuses around the country as students return from summer break.