Man and woman kill two police officers in restaurant before fatally shooting a third person and then killing themselves.

The Las Vegas Walmart where the pair shot a third victim before killing themselves.

A man and a woman have shot and killed two police officers in the US city of Las Vegas before fatally shooting a third person and then killing themselves, police say.

The pair on Sunday walked into CiCi's Pizza restaurant and shot at point-blank range officers Alyn Beck, 42, and Igor Soldo, 32, who were eating lunch, Las Vegas police said.

One of the officers was able to fire back before he died, but it was unclear if the suspects were hit, Sheriff Doug Gillespie of the Las Vegas Metro Police Department said at a news conference on Sunday afternoon.

The suspects then fled to a Walmart store across the street, where they fatally shot a person inside the front door and exchanged gunfire with police before killing themselves in an apparent suicide pact.

The female suspect then shot the male suspect before killing herself, Gillespie said. The victim's identity has not been confirmed, and the suspects' names have not been released.

Both officers were taken to the hospital, but it was unclear if they died there or at the scene.

"It's a tragic day," Gillespie said. "We have a community to protect, we will do it with our heads held high."

One of the suspects yelled, "This is a revolution," but the motive for the shooting remains under investigation, Las Vegas police spokesman Larry Hadfield told The Associated Press. He said: "We don't know anything about the suspects yet.''

Assistant Sheriff Kevin McMahill said the male suspect yelled "everyone get out'' before shooting at Walmart. The suspects then walked to the back of the store.

Walmart employees and shoppers were taken to a nearby clothing store to be interviewed by police.

The restaurant and Walmart remained closed as detectives processed evidence. McMahill said the investigation was "very complex'' because it involved more than 1,000 witnesses.

Governor Brian Sandoval issued a statement saying he was devastated by the murders of the two officers and an "innocent bystander".