Just as tensions in one corner of the South China Sea died down, another standoff is threatening to shake the already tense region.

According to Reuters, the Chinese military has set up ‘combat-ready’ patrols in disputed waters in response to Vietnam’s air patrols, after the country claimed the Spratlys Island, citing its maritime laws.

Defence Ministry spokesman Geng Yansheng told the Financial Times that China would “resolutely oppose any militarily provocative behaviour” to protect its national sovereignty and security and promote development interests in seas ‘under China’s control’.

Just last week, China and Vietnam met in a maritime law battle after Vietnam claimed the Spratlys Islands as its own; the islands are also claimed by a handful of other Asian countries. Tensions escalated after Chinese offshore oil specialist, Cnocc, invited foreign investors to explore oil resources in the disputed waters, laying its own claim. Vietnam condemned the plan, saying it was “illegal”.