BEIJING (AP) — China says a branch of its coast guard is holding live-firing exercises in the Tonkin Gulf amid tensions among disputants to territory in the South China Sea.

The Maritime Safety Administration said ships and boats were barred from the area between the southern province of Hainan and the northern coast of Vietnam from Monday to Wednesday.

China has held several military exercises in surrounding waters since an international arbitration panel last month issued a ruling invalidating China’s claim to virtually the entire South China Sea.

On Sunday, China said its planes and ships held war games in the Sea of Japan last week, during which it deployed its latest-generation frigate.

China plans joint naval exercises with Russia in the South China Sea next month in a move criticized by U.S.