A shooting at a school in Minneapolis that left two children dead and 17 others injured is being investigated as an anti-Catholic hate crime, the FBI says.

The FBI is investigating this shooting as an act of domestic terrorism and hate crime targeting Catholics, FBI Director Kash Patel said in a post on X.

The two children, aged eight and ten, were killed when an attacker opened fire through the windows of the city's Annunciation Church on Wednesday morning as children were celebrating Mass.

The attacker, who died at the scene of a self-inflicted gunshot wound, was later named by police as 23-year-old Robin Westman.

Authorities have yet to release a suspected motive for the attack.

A constant stream of mourners arrived at the scene on Wednesday night, some leaving flowers. There was a sense of shock and anger that this had happened at the start of a church Mass ushering in the new school term.

Pope Leo XIV, the first American pope, was among those who paid tribute to the young victims, saying he was 'profoundly saddened' by the attack.

Police Chief Brian O'Hara told reporters: '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,' he said.

Police began receiving calls of a shooting just before 08:00 local time (13:00 GMT) on Wednesday. The attacker approached the side of the church, which also houses a school, and fired dozens of shots through the windows using three firearms - a rifle, a shotgun, and a pistol. Police also found a smoke bomb at the scene.

Investigators are examining if the suspect fired inside the building or if all shots came from outside the church, noting that no bullet casings were found inside.

A 10-year-old boy who survived the attack told CBS affiliate WCCO that his friend saved him from bullets by lying on top of him. 'I was like two seats away from the stained glass window,' he said. 'My friend, Victor, saved me though, because he laid on top of me, but he got hit.'

Westman's mother previously worked at the school, as indicated in a school newsletter from 2016. The attacker legally changed their name in 2020, publicly identifying as female. This has led to discussions and pushback against hatred directed towards the transgender community in the wake of the attack.

In a press conference, Minneapolis Mayor Jacob Frey expressed the need for unity against such acts of violence and hate, emphasizing the importance of supporting the community during this difficult time.