President Joe Biden in grieving the loss of life in Maine and is praying for the injured, White House national security spokesperson John Kirby told MSNBC.

Kirby urged Congress to do more to ban semi-automatic rifles, which he called weapons of war allowed on the streets, and said that Biden's recent legislation, the Safer Communities Act, was a start -- but not enough.

The Safer Communities Act included incentives for states to pass red flag laws, closed the so-called boyfriend loophole and created an enhanced background check process for people under 21 who are looking to buy firearms from licensed dealers. Biden himself, while signing the bill, said it wasn't everything he wanted but was a start.

Biden has ordered flags to be flown at half-staff in honor of the Maine victims.

Attorney General Merrick Garland said in a statement, "I am heartbroken for those who have lost loved ones, for those who have been injured, and for the entire Lewiston community."

"The FBI, ATF, and U.S. Marshals are on the ground to provide investigative support and victims assistance services to our law enforcement partners in Maine," he said. "No community should have to endure the horrific mass shootings that have become routine in our country."

The person of interest in the Maine mass shooting, Robert Card, has been an Army reservist since December 2002, the Army said.

He has no combat deployments, the Army said.

His current rank is sergeant first class. His job is listed as petroleum supply specialist.

The police chief in Lisbon, Maine, told reporters Thursday that no tip is too small in the hunt for Robert Carr, the person of interest in the Lewiston, Maine, mass shooting.

Lisbon borders Lewiston and is where authorities are searching for the person of interest.

The white Subaru believed to be linked to the person of interest was found in Lisbon.

"If you see something in Lisbon, that is suspicious, I want you to call," Chief Ryan McGee said.

The chief said that police had responses from agencies all across the state and their federal partners.

He said he sent every one of his available officers to the neighboring community before the situation came to Lisbon.

-ABC News' Luke Barr

Municipal offices in Lewiston and Lisbon, Maine, will be closed on Thursday, officials said.

In Lewiston, where the mass shooting occurred, officials said they would also close the library and cancel all events, including early voting, at city buildings.

"Non-emergency personnel should stay at home tomorrow too," the city said in a social media post.

The nearby town of Lisbon, where police sources said the person of interest's Subaru had been traced, also closed municipal buildings on Thursday.

"Please prioritize safety and continue to shelter in place," Lisbon officials said in a notice on the town website.

Maine mass shooting suspect Robert Card allegedly behaved erratically this summer while serving as an Army reservist, according to a defense official.

Card was deployed to Camp Smith Training Center in upstate New York to help support summer training for West Point cadets.

Card allegedly threatened other soldiers with violence, according to a source briefed on the situation.

"Out of concern for his safety, the unit requested that law enforcement be contacted," the defense official said. Police took Card to Keller Army Community Hospital at the United States Military Academy for a medical evaluation, the official said.

Sometimes this spring or summer, Card bought an accessory to a firearm, according to the source briefed on the situation.

With the manhunt for Card ongoing, the source noted that Card owns a boat and property in the Lewiston area.

-ABC News' Luis Martinez and Pierre Thomas