One of the attackers yelled "This is the start of a revolution" before shooting the officers and stripping them of their weapons and ammunition, the Las Vegas Review-Journal said.
Two officers were shot by the gunmen -- a man and a woman -- as they ate lunch at CiCi's Pizza, it said, citing police sources. One of the officers died at the scene, while the second subsequently died in surgery.
The attackers then headed to a nearby Walmart store, exchanging gunfire with and ultimately killing a civilian who was carrying a concealed weapon.
The male shooter, described as a tall white man, yelled "everyone get out" before shooting, said Assistant Sheriff Kevin McMahill.
Earlier, police alerted the public on their Twitter feed.
"We're investigating a multiple shooting at the 300 block of N Nellis. Persons have been injured. Avoid the area. Please RT. #Vegas," the Las Vegas Metropolitan Police Department said on Twitter.
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