HANOI, Vietnam (AP) -- Vietnam has accused a Chinese vessel of firing a flare on a Vietnamese fishing boat that set its cabin alight in the disputed South China Sea, where rival claims to gas-rich waters have strained relations between the countries.
The Vietnamese government did not say if anyone was injured in the incident last Wednesday but called it "very serious." It lodged a formal complaint with the Chinese Embassy in Hanoi.
The United States also said it was concerned by the incident, and was seeking information about it from both sides.
The fishing boat was near the Paracel islands when an unidentified Chinese vessel chased it and fired the flare, the government said in a statement issued late Monday.
Hanoi demanded that China punish those responsible and pay reparations to the fishermen whose boat was damaged.
Chinese Foreign Ministry spokesman Hong Lei said China had taken unspecified but "legitimate and reasonable" actions against Vietnamese boats working illegally in Chinese waters. He denied that any boats had been damaged, but gave few other details.
There have been other clashes in the waters, often related to claims of illegal fishing or violations of Chinese unilaterally imposed fishing moratoriums.
Vietnam and China each claim large parts of the South China Sea. The Philippines, Malaysia, Taiwan and Brunei also maintain that parts of the sea are theirs.
The profile of the long-running disputes has been raised in recent years because of China's economic and military growth and subsequent American interest. The Paracels, which were occupied by China shortly before the end of the Vietnam War in 1975, is a particular flashpoint.
"We strongly oppose the threat or use of force or coercion by any claimant to advance its claims in the South China Sea," U.S. State Department spokesman Patrick Ventrell said in Washington.
He said it underscored the need for a code of conduct for dealing with disputes there in a "transparent and rules-based way."
China last year incorporated the Paracels and most of its other South China Sea claims within the newly declared Sansha city-level administrative unit as way of raising the region's profile and increasing funds for infrastructure and economic development.
China is also boosting its civilian fisheries and maritime surveillance patrols in the area. China's navy also conducts missions in the South China Sea, although it has sought to keep military units out of conflict zones to avoid elevating tensions.
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