The statement was among the sharpest-worded Vietnam has issued in the two countries' increasingly tense disputes over maritime territory in the South China Sea.

Vietnam issued the demand after China notified the Vietnamese embassy in Beijing on Tuesday that it was fining the fishermen for allegedly using explosives to fish, and would release them only after the fine was paid.

Vietnam's Foreign Ministry said China originally notified it on September 15 that the fishing boat had been detained for violating Chinese territorial waters, and that no mention had been made of explosives until yesterday.

The ministry called the Chinese fine "irrational."

The boat was seized by Chinese naval patrols on September 11. Vietnamese authorities say coastal guards inspected it before it embarked, and that there were no explosives on board.

A coastal border guard official at the vessel's home port of Ly Son, who asked to remain anonymous, said the Chinese had demanded a fine of 70,000 yuan (10,500 dollars). The official said the boat owner's wife lacked the funds to pay the fine.

Vietnam, China, and four other nations dispute sovereignty over the Spratly and Paracel Islands and the surrounding waters, which are believed to be rich in undersea mineral resources. In the past year, China has seized or detained hundreds of Vietnamese fishing boats in disputed waters.

Deutsche Presse Agentur - October 6, 2010