() Annunciation Catholic School in Minneapolis remained closed Thursday as officials continued to investigate a shooting that left two children dead and 17 people injured.

Police said a gunman approached the school’s church around 8 a.m. local time and began shooting into the building, as children and adults gathered for Mass marking the start of the school day.

The children killed were 8 and 10 years old, according to officials. All the injured parishioners are expected to survive.

“These beautiful children at Annunciation, they should not have to go through this right now. They should be learning math and playing at recess and messing around in a cafeteria and playing with their friends. That’s what childhood is about,” said Minneapolis Mayor Jacob Frey.

Minnesota gunman had ‘manifesto,’ but motive unknown

The shooter, identified by authorities as 23-year-old Robin Westman, died on the scene.

The weapons used in the attack were legal, and gun magazines had phrases such as “Kill Donald Trump” and “Where is your God?” written on them, according to police.

Minneapolis Police Chief Brian O’Hara said Westman had “some sort of manifesto that was timed to come out on YouTube.”

He said the video has since been taken down, and that investigators are examining the footage to try to determine a motive.

Photos: Candlelight vigils held for Minnesota shooting victims

White House reacts to Minnesota shooting

President Donald Trump has not yet commented on the reported messages referencing him, but he called Wednesday’s shooting “tragic” and ordered flags at half-staff until Sunday at sunset.

First lady Melania Trump also weighed in, calling for more action to stop school shootings.

“To prevent future tragedies, it is crucial we look into behavioral threat assessments across all levels of society beginning in our homes, extending through school districts and of course, social media platforms, she wrote on social media. “Being aware of these warning signs and acting quickly can save lives and make American communities safer.”

FBI Director Kash Patel called the shooting an “act of terrorism and a hate crime targeting Catholics,” though the Minneapolis police chief has said several times there has been no conclusion on a motive.