BANGKOK, Thailand: Chinese authorities said they started live-fire military exercises in the Gulf of Tonkin this week, just days after Vietnam announced a new boundary marking what it sees as its territory in the waters between the two countries.

China's Maritime Safety Administration said the drills would focus on the Beibu Gulf, closer to China's side of the Gulf of Tonkin, and would continue until February 27 evening. No other details were provided. The exercises follow Vietnam's announcement of a new baseline to measure the width of its territorial waters in the Gulf, which is in line with the U.N. Convention on the Law of the Sea. Vietnam said this move strengthens its legal claim to the area but has not yet responded publicly to China's drills.

China and Vietnam have had a maritime agreement over the Gulf of Tonkin for years but often clash over claims in the nearby South China Sea, especially around the Spratly and Paracel Islands. China has recently taken a more aggressive stance, including an incident in October where Chinese forces attacked Vietnamese fishermen near the Paracel Islands, injuring three.

China claims nearly the entire South China Sea, though it has not clearly defined its exact boundaries, only offering a map with ten dashed lines outlining its claimed territory. These claims overlap with those of Vietnam, the Philippines, Malaysia, Brunei, and Taiwan. Indonesia has also had confrontations with Chinese coast guards near the Natuna Islands.

Tensions are especially high with the Philippines, with frequent clashes between their forces. Last week, a Chinese navy helicopter flew within 10 feet (3 meters) of a Philippine patrol plane near the disputed Scarborough Shoal.

Australia and New Zealand also criticized China for conducting live-fire drills between their countries with little warning, forcing flight diversions. While China didn't break international laws, officials said they were given only a few hours' notice instead of the usual 12 to 24 hours.