Two US police officers and a first responder were shot dead when responding to a call for help from a home in suburban Minneapolis.
A suspect also died, officials said, after the incident in Burnsville, Minnesota, which was ringed with police cars that kept the press and public away from the scene.
The deaths of the two Burnsville police officers and the first responder were confirmed by the Minnesota Police and Peace Officers Association (MPPOA).
The association said negotiations with a suspect went on for four hours before a Swat team entered the home in Burnsville.
Seven children were inside the home. It was not known if any were harmed.
Details on how the suspect died were not immediately released.
City officials identified the killed officers as Paul Elmstrand and Matthew Ruge, both 27, and the firefighter and paramedic was named as Adam Finseth (40).
Another police officer, Sgt Adam Medlicott, was injured and taken to hospital with what are believed to be non-life-threatening injuries, the city said.
“We are heartbroken. Our law enforcement community is heartbroken. We’re just devastated at the horrific loss,” Brian Peters, executive director of the MPPOA, which represents public safety professionals in the state, said in a statement.
The shooting happened in a tree-lined neighbourhood with two-storey homes. A police armoured vehicle parked nearby had bullet damage to its windshield, but there was no confirmation on whether that was the result of the incident.
The street was lined with police cars, firefighters and ambulances.
Police scanner recordings on Broadcastify.com capture a rattled man saying “I need any ambulance” as he struggled to catch his breath. Someone could later be heard talking about three being loaded into ambulances, uttering the word “critical”.
“We must never take for granted the bravery and sacrifices our police officers and first responders make every day,” Minnesota governor Tim Walz said. “My heart is with their families today and the entire state of Minnesota stands with Burnsville.”
Other law enforcement agencies immediately began posting messages of condolence on social media, including images of badges with blue bars through them, as a mark of solidarity in mourning.
Law Enforcement Labour Services, which represents rank-and-file officers and the supervisors of Burnsville Police Department, said in a statement that “thoughts and prayers are with the family of the officers and first responder”.
“These officers were struck down while answering the call of duty to serve and protect. We mourn alongside the Burnsville community and the families of those killed,” said the statement from executive director Jim Mortenson.
The State’s Bureau of Criminal Apprehension said in a news release that it had been asked to investigate the shooting and added that the inquiry was in the early stages.