A man shot dead four people and wounded nine others in an attack on Monday at a bank in downtown Louisville, Kentucky, city officials said. The shooter was fatally shot at the scene, the city’s police department said, but it was unclear whether from police gunfire or a self-inflicted wound.

The shooter was a current or former employee of the bank, Paul Humphrey, a Louisville Metro Police Department deputy chief, told reporters.

Police said they responded within minutes to reports of an attacker at about 12:30 GMT at an Old National Bank branch near Slugger Field Baseball Stadium in the city’s downtown. Officers fired at the shooter, police said.

The man was armed with an “AR-15-style” semiautomatic rifle, CNN reported, citing an unnamed federal law enforcement official.

Nine people wounded in the attack were treated at the University of Louisville hospital, a hospital spokesperson said, including two police officers. One of the police officers was in critical condition, police said.

“We will come together as a community to work to prevent these horrific acts of gun violence from continuing here and around the state,” Craig Greenberg, mayor of the city of 625,000, told reporters at a briefing.

Kentucky Governor Andy Beshear, on the verge of tears, said during the briefing that he knew some of the victims.

“I have a very close friend that didn’t make it today,” Beshear said, “and one who’s at the hospital that I hope is going to make it through.”

Mass shootings have become recurrent in the United States. So far this year, the nation has experienced 146 mass shootings – using the definition of four or more shot or killed, not including the shooter – according to the Gun Violence Archive, a non-profit group.

In one of the most recent high-profile incidents, three 9-year-old students and three staff members were killed by a former student at a school in Nashville, Tennessee, on March 27.

• A Reuters report