Four law enforcement officers have been fatally shot and four others were wounded while serving an arrest warrant in Charlotte, North Carolina.
A suspected attacker was found dead in the front yard of a barricaded home after a standoff that lasted three hours, police said.
Two other persons of interest were taken into questioning, authorities added.
It is one of the deadliest assaults on US law enforcement in recent years.
The officers were part of a US Marshals Service-led task force. The warrant they were attempting to serve on Monday was against a felon wanted for illegally possessing a firearm.
Gunfire erupted on the suburban street as they tried to do so.
The 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 told a news conference. A high-powered rifle was found inside the property, he added.
He said it was the worst attack on police officers he could recall in his 30 years on the force.
Shots were still ringing out more than two hours after the attack began in a residential area in the east of the city, according to witnesses.
The assault ended when police stormed the home on Galway Drive in the Shannon Park neighbourhood, using armoured vehicles to smash their way in, destroying windows and doorways.
Two women who were inside the home with a suspect were taken in for questioning, police said. Police believe there was more than one attacker involved in the incident.
The US Marshals Service confirmed in a statement that one of its officers had been killed in the raid.
North Carolina Governor Roy Cooper said two of the officers killed were members of the state’s Department of Adult Corrections (NCDAC).
They were identified as Sam Poloche, who joined NCDAC in 2013, and William “Alden” Elliott, who joined in 2016.
Also killed was Charlotte-Mecklenburg Police Department Officer Joshua Eyer, who had served on the force for six years, police said.
The dead suspect was later identified by police as 39-year-old Terry Clark Hughes Jr, who was wanted for possession of firearm by a felon.
Chief Jennings said on Monday afternoon: “A lot of the questions that need to be answered, we don’t even know what those questions are now.
“We have to get a full understanding of why this occurred and also uphold 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 ambulance rescues.
Witness Tyler Wilson told CBS News he was working at home when he heard police shout for the suspect to come out of the house.
Charlotte Mayor Vi Lyles said in a statement that she was “deeply saddened” by the shooting.
She added she spoke to President Joe Biden, who passed his condolences to the community.
In a statement later on Monday night, Mr Biden called the officers “heroes who made the ultimate sacrifice, rushing into harm’s way to protect us.”
He also urged Congress to take action on “the scourge of gun violence” by banning assault weapons and high-capacity magazines.
