Lewiston, Maine - Robert Card, a 40-year-old soldier in the US Army Reserve, is suspected of gunning down 18 people in a horrific mass shooting in Lewiston, Maine.

The attack, which targeted a bowling alley and a bar in Lewiston on Wednesday night, is one of the deadliest since 2017, when a gunman opened fire on a crowded music festival in Las Vegas, killing about 60 people.

Authorities have issued a warrant to arrest Card for murder, Colonel William Ross of the Maine State Police told a press conference Thursday, adding that he is considered "armed and dangerous" and warning people not to approach him.

The Lewiston police department released images of a bearded man dressed in a brown hoodie and blue cargo pants and armed with an assault rifle.

Card, born in 1983, is a certified firearms instructor and a member of the US Army Reserve, according to multiple law enforcement sources.

The US Army provided AFP with details on Card's military service, saying he is a sergeant first class in the Army Reserve with "no combat deployments" who enlisted in December 2002.

Card is a Petroleum Supply Specialist, which entails supplying the Army "with the fuel it needs to maintain a state of readiness at all times," according to a US military career website.

The information on Card's service history did not mention him being a firearms instructor, though it's possible he was in a civilian rather than military capacity.

According to ABC News, Card spent two weeks at a mental health facility earlier this year after allegedly threatening to carry out a shooting at a National Guard facility.

NBC News also referred to a threat to a National Guard installation, citing a law enforcement bulletin as saying Card "recently reported mental health issues to include hearing voices and threats to shoot up the National Guard Base" in Saco, Maine.

Officials at Thursday's press conference would not elaborate on the reports, however, saying they did not yet know the motive behind the killings.

Maine resident Liam Kent told NBC that he grew up near Card and his family, who he described as "gun fanatics" and "very much associated with right-wing militias."