Vietnam’s National Assembly approved a law on June 21 laying sovereignty claims on disputed islands in the South China Sea, which China “vehemently opposed”, underlining Beijing’s aggressiveness in claiming territories in the region.

According to Asahi Shimbun, Vietnam recently approved a new Maritime Law which declares sovereignty and jurisdiction over the Paracel and Spratly Islands, which means that foreign vessels will have no rite of passage through the waters.

China said that Vietnam’s law is “a serious violation of China’s territorial sovereignty.” Vice Foreign Minister Zhang Zhijun summoned Ambassador Nguyen Van Tho, pressing the diplomat for an “immediate correction” and saying that the law is null and void. Zhang added that “China demands the Vietnamese side … not do anything to harm relations or the peace and stability of the South China Sea”.

China claims most of the South China Sea, including islands near other Asian countries’ coastlines. Beijing says that the Spratly Islands and Scarborough Shoal have been part of its territory since they was discovered in early history.

China has been caught in a standoff with the Philippines in the Scarborough Shoal. Both countries have deployed a number of vessels to lay sovereignty over the potentially resource-rich islands.