Media playback is unsupported on your device Media caption An eyewitness said the gunman declared he was taking part in "a revolution"

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 killing themselves.

Police say there are no other suspects in the shooting.

'Tragic day'

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.

Image copyright Reuters Image caption The attack took place in a pizza cafe at Sunday lunchtime

Image copyright Getty Images Image caption The suspects later killed themselves in a nearby Walmart

Image copyright Reuters Image caption The colleagues of the two dead police officers were devastated by the murders

There was no obvious motive for the shootings.

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."