May 23 (UPI) -- Three Vietnamese fishermen died after a mysterious explosion in the South China Sea, according to a Vietnamese press report.
The news of the explosion comes at a time when China is stepping up militarization of disputed islands in international waters and chased out 10 fishing boats of foreign origin.
VN Express reported Wednesday the explosion took place Sunday near the Paracel Islands, where China is believed to have recently tested the takeoff and landing capabilities of its bombers.
The islands are also claimed by Vietnam.
The three Vietnamese fishermen were part of a 13-member crew at sea in a small basket boat to catch sea cucumbers.
The explosion occurred when the trio pulled up an unfamiliar object that then detonated, according to the Vietnamese press report.
News of the bomb, possibly of Chinese manufacture, has since then spread through Vietnamese social networks.
China has made it clear the Paracel Islands are part of its sovereign territory and that the South China Sea, within its unilaterally designated nine-dash line, is under its control.
Beijing's navy recently chased out 10 foreign vessels to "safeguard maritime interest," according to People's Liberation Army Daily.
Vietnam's deputy minister of national defense Le Chiem said the Chinese have been fishing in Vietnamese waters, while accompanied by "special forces."
"There were times when several tens of fishing boats, under the support of Chinese law enforcement forces, declared that the waters were theirs and chased Vietnamese fishers away," Chiem said.
Chinese actions follow a Vietnamese decision to allow Russian oil firm Rosneft to begin drilling in waters claimed by China, according to Chinese analysts who spoke to the South China Morning Post.
China continues to promote its military presence on reclaimed islands.