Two people have shot and killed two police officers in the US city of Las Vegas, before killing another person and then shooting themselves.
The incident began in a pizza cafe at 11:30 (18:30 GMT) on Sunday, when a man and a woman shot at the two officers who were having lunch.
They then entered a Walmart shop nearby and shot one person dead, before committing suicide.
Police say there are no other suspects in the shooting.
The woman shot her male companion before turning the gun on herself, Sheriff Doug Gillespie of the Las Vegas Metro Police Department said at a news conference.
However, eyewitnesses said the attackers shouted "This is a revolution" as they entered Cici Pizza and shot the police officers.
"I think in any case where people are ambushed and shot is upsetting to the public," police spokesman Larry Hadfield told the Associated Press.
"We don't know anything about the suspects yet and are trying to learn more."
Nevada Governor Brian Sandoval later said he was devastated by the murders of the two police officers - Alyn Beck, 42, and Igor Soldo, 32 - and an innocent bystander.
One of the officers reportedly managed to return fire in the cafe, and there was a further exchange of fire between police and the suspects in Walmart.
"It's a tragic day," Sheriff Gillespie said.
"We have a community to protect, we will do it with our heads held high."