Four Chinese fisherman were shot and murdered, while another three were wounded near the disputed Spratly Islands in the South China Sea.
The men from the island province of Hainan were attacked April 27, while they were fishing, the official Xinhua News Agency said.
The nationality of the attackers is unknown, Xinhua said. All the equipment on the boat, including radios and navigation apparatus, was taken, it said.
An investigation was under way, Xinhua said.
Four of the men died on the spot and the three were rescued and have been hospitalized, it said.
The Spratly Islands are claimed in whole or in part by Vietnam, China, Taiwan, the Philippines, Malaysia and Brunei. They are believed to be rich in oil and gas reserves.
The conflicting claims have led to a series of squabbles, including a 2002 incident when Vietnam fired warning shots at Philippine military planes and a number of spats over fishermen crossing into the wrong waters.