Four people were killed and eight others were wounded in a shooting at a bank in Louisville, Kentucky, Police said on Monday.
Louisville Metro Police Department Deputy Chief Paul Humphrey told reporters that the shooter was also killed and appeared to be a former employee of the Old National Bank.
He said at least eight people were being treated for injuries, including two police officers. One officer and another of the wounded were in critical condition.
"We believe this is a lone gunman involved," Humphrey said.
Senate Republican Leader Mitch McConnell, who represents Kentucky, wrote on Twitter that he was "devastated" by the news and offered "thoughts and prayers" for the families of the victims and the city.
Posts on social media showed that police arrived and were at the scene minutes after receiving the emergency call.
They had initially put the death toll at five, but later clarified that number included the shooter.
According to the Gun Violence Archive, the Louisville incident was the 146th mass shooting, defined as incidents in which four or more people were shot or killed, in the United States this year.
It happened just two weeks after a former student killed three children and three adults at a Christian elementary school in Nashville, about 160 miles (260 km) to the south.
Efforts to tighten gun control in the US are facing opposition from Republicans, despite public outrage over the shootings.