Vietnam's foreign ministry expressed outrage at China's plans to commence drilling for oil this week in waters claimed by both countries. The area in question lies near the Paracel Islands, or roughly 120 nautical miles east of Vietnam's South China Sea coast.

"All foreign activities in Vietnam's seas without Vietnam's permission are illegal and invalid," the foreign ministry said in a statement. "Vietnam resolutely protests them."

According to Hanoi, the disputed waters belong to Vietnam's exclusive economic zone as defined by the 1982 UN Convention on the Law of the Sea. However, Beijing seized the islands - known as Hoang Sa in Vietnam and Xisha in China - in 1974 and has controlled them ever since.

The statement by Vietnam's foreign ministry followed a warning from China's Maritime Safety Administration over the weekend that prohibited all ships from entering the 3-mile (4.8-kilometer) radius surrounding the drilling area until operations end on August 15.

Beijing's increased activities in contested waters this year, as well as its increased investment in its military, have worried China's neighbors. It is currently involved in territorial disputes with not only Vietnam, but also Japan, Malaysia and Philippines.

US, Philippines begin military drill

Meanwhile, US and Philippines troops launched a 10-day military drill on Monday. Over 5,000 soldiers from both sides took part in the largest of their annual war games.

At the commencement ceremony released on Monday, Filipino Foreign Secretary Albert del Rosario described the exercise as a necessary step toward dealing with "aggressive" neighbors.

"In recent years, tensions in the Asia-Pacific region have increased due to extensive and expansive maritime and territorial claims understanding the rule of law," del Rosario said. "Aggressive patterns of behavior changing the status quo threaten peace and stability in the region."

Last week, US President Barack Obama and Philippines President Benigno Aquino III signed a defense pact, which will see an increase of US troops deployed to the Pacific island nation. Although the two countries already have a mutual defense treaty, the move was seen as a pledge of US support against military aggression in the region.

kms/jr (AP, AFP, dpa)