Vietnam announced a live ammunition drill yesterday in an apparent response to China's demand that the Vietnamese halt all oil exploration in the South China Sea.

Vietnam said its navy would carry out two exercises lasting a total of nine hours in an area in the South China Sea on Monday.

The announcement posted on the state-owned Northern Maritime Safety Corp's website warned boats and ships to stay out of the area.

It was the first time Vietnam had issued such an alert about maritime drills and it came a day after China demanded that Vietnam stay out of China's territorial waters.

China had accused Vietnam of illegally entering its waters and endangering Chinese fishermen's lives around the South China Sea's Nansha Islands. Vietnam had earlier accused a Chinese fishing boat of damaging a cable of a seismic survey boat operated by PetroVietnam.

But the Chinese Foreign Ministry said the Chinese fishing boat crew were merely protecting themselves after their boat was dragged backward for more than an hour by the Vietnamese vessel.

Ministry spokesman Hong Lei said Vietnam had been illegally exploring for oil and gas in Chinese territory and demanded it stop all acts which violated China's sovereignty.

China has indisputable sovereignty over the Nansha Islands and the surrounding waters, Hong said, adding that Chinese fishermen had been fishing in the area for generations.

However, Chinese boats had been chased away by armed Vietnamese ships on Thursday morning. Amid the ensuing turmoil, a fishing net got tangled up in the cables of the Vietnamese oil exploring vessel operating illegally in the area. The fishermen were forced to cut their net.

The incident had "seriously endangered the safety of the Chinese fishermen," Hong said.