Authorities say four law enforcement officers were shot and killed and four others wounded during a warrant operation in Charlotte, North Carolina.
At least one suspected attacker was found dead in the front yard of a barricaded home after a three-hour standoff, police said.
Authorities said two armed suspects were involved.
It was one of the deadliest attacks on US law enforcement in decades.
The officers were part of a task force led by the U.S. Marshals Service who were trying to serve a warrant against a felon wanted for illegal gun possession when gunfire erupted on a suburban street Monday.
Officers returned fire at an assailant in the front yard, then more shots were fired at them from inside the home, Charlotte-Mecklenburg Police Chief Johnny Jennings said at a news conference. A high-powered rifle was found inside the property, he said.
“Today we lost some heroes who tried to keep our community safe,” the police chief told reporters.
He said it was the worst attack on police officers in his 30 years on the force.
According to witnesses, shots were still ringing more than two hours after the attack began in a residential area in the east of the city.
The attack ended when police entered the home on Galway Drive in the Shannon Park neighborhood, using armored vehicles to break in and smash windows and doors.
Police said two other people inside the home with the suspect — a woman and a 17-year-old boy — are being questioned. At least one of them is believed to have fired at officers.
The US Marshals Service confirmed in a statement that one of its officers was killed in the attack.
North Carolina Governor Roy Cooper said two of the slain officers were from the state's Department of Adult Corrections.
“Our hearts go out to the families and colleagues of the officers in today's horrific attack,” he posted on X, formerly Twitter.
Also killed was Charlotte-Mecklenburg Police Department Officer Joshua Ayer, who had been on the force for six years, police said.
“We are forever indebted to Officer Iyer's bravery and ultimate sacrifice,” the police statement said.
Chief Jennings said Monday afternoon: “There are so many questions to be answered, we don't even know what those questions are.
“We need to gain a fuller understanding of why this happened and uphold the integrity of the investigation.”
Several nearby schools were locked down during the siege.
Residents were asked to stay in place and nearby streets — including Interstate 77 — were closed to facilitate an ambulance rescue.
Witness Tyler Wilson told CBS News that he was working around the house when he heard police yelling at the suspect to come out of the house.
After that there was just confusion, he said. “Shoots rang out left and right.
“We had SWAT, US marshals set up snipers in our bedrooms. There was an officer [that] He was dragged by his arms through our house.”
“It was pretty crazy,” he continued. “It was about 30 minutes where it was a straight shootout.”
Charlotte Mayor V Lyles said she spoke with President Joe Biden, who offered his condolences to the community.
The mayor said in a statement that he was deeply saddened by the shooting.