Four Chinese nationals have been stabbed to death in Papua New Guinea in what the South Pacific island nation's prime minister has condemned as a "brutal and cowardly" attack.

National police spokesman Dominic Kakas says the three men and one woman were killed Monday night at a shop they ran in Port Moresby, the capital. Kakas says the assailants entered through the back door and stabbed the victims with knives.

Papua New Guinea Prime Minister Peter O'Neill vowed in a statement Wednesday to bring the killers to justice.

Kakas says the victims are believed to be related. Police don't know where in China they are from or how long they were in Papua New Guinea.

Police have questioned several people, including workers at the shop, but have made no arrests.