Four law enforcement officers were shot to death and four others were injured while executing a warrant in Charlotte, North Carolina, authorities said.
Police said at least one suspected assailant was found dead in the front yard of a barricaded home after a standoff that lasted three hours.
Authorities said two armed suspects were involved.
This is one of the deadliest attacks on US law enforcement in decades.
The officers were part of a special unit led by the U.S. Marshals Service and were attempting to execute a warrant against a felon wanted for illegally possessing a firearm when a shooting occurred on a suburban street Monday.
Charlotte-Mecklenburg Police Chief Johnny Jennings said at a news conference that officers fired back at the assailants in the front yard, then more shots were fired from inside the home. He added that a high-powered rifle was found on the premises.
“Today we lost some heroes who were out just trying to keep our community safe,” the police chief told reporters.
He said it was the worst attack on a police officer he could recall in his 30 years on the job.
Witnesses said gunfire still rang out in residential areas in the eastern part of the city more than two hours after the attack began.
The assault ended with police raiding a home on Galway Drive in the Shannon Park area, using an armored vehicle to gain entry and smashing windows and doorways.
Two other people who were in the house with the suspect, a woman and a 17-year-old boy, are also being questioned, police said. At least one of them appears to have fired at the police.
The U.S. Marshals Service confirmed in a statement that one officer was killed in the attack.
North Carolina Gov. Roy Cooper said two of the slain officers were members of the state's Department of Adult Corrections.
“Our hearts go out to the families and colleagues of the police officers who suffered today's brutal attack,” he posted on X (formerly Twitter).
Police said Joshua Eyer, a Charlotte-Mecklenburg Police Department officer of six years, was also killed.
“We are forever grateful for Officer Eyer's courage and ultimate sacrifice,” police said in a statement.
“Many of the questions that need to be answered, we don't even know what those questions are at this point,” Chief Jennings said Monday afternoon.
“We need to fully understand why this happened, and we need to maintain the integrity of the investigation.”
Several nearby schools were placed on lockdown during the siege.
Residents were asked to shelter in place, and nearby streets, including Interstate 77, were closed to facilitate emergency rescue.
Eyewitness Tyler Wilson told CBS News that he was working from home when he heard police yelling for the suspect to come out of the house.
“After that it was just chaos,” he said. “There were gunshots ringing out left and right.
“We had swats in place and the federal marshals set up snipers in our bedroom. There were cops.” [that] His arm dragged me through the house. ”
“It was pretty crazy,” he continued. “It was a straight shootout for about 30 minutes.”
Charlotte Mayor Vi Lyles said she spoke with President Joe Biden, who expressed his condolences to the community.
The mayor said in a statement that he was “deeply saddened” by the shooting.