WASHINGTON

A shooting at a bank in the US city of Louisville, Kentucky left four people killed with eight others injured, including two responding police officers, authorities said Monday.

The shooter was confirmed dead at the Old National Bank in downtown Louisville, but the circumstances of the gunman's death remain unclear, Metro Police Deputy Chief Paul Humphrey told reporters.

The gunman appears to have been a previous employee at the bank, Humphrey said.

All of the injured have been transported to the University of Louisville Hospital. One of the officers who was injured is in critical condition and is undergoing surgery at the hospital, according to the deputy police chief. Another injured victim remains in critical condition.

The FBI's local field office said its special agents have been sent to the scene of the shooting, and are actively assisting local law enforcement in the ongoing investigation.

Officers arrived at the bank within minutes of calls coming in reporting an "active aggressor," police said.

Humphrey said officers exchanged gunfire with the gunman upon arriving at the bank. It is unclear if the suspect was killed by the responding officers or if he fatally shot himself.

"It is clear from the officer's response that they absolutely saved people's lives. This is a tragic event, but it was the heroic response of officers that made sure that no more people were more seriously injured than what happened," said Humphrey.

Gov. Andy Beshear said the "senseless act" took the lives of Kentuckians, including, he said, personal friends of his.

"What these families are experiencing is unimaginable. They need us to wrap our arms around them and to love them with all our hearts," Beshear said on Twitter.

"Thank you to the heroic members of the LMPD (Louisville Metro Police Department) and all of our first responders who undoubtedly saved lives while putting their own at risk. We are forever grateful," he added.