The Philippines has enlisted “foreign forces” to patrol the South China Sea and has been stirring up trouble, China’s military said on Thursday, referring to joint patrols this week by Philippine and U.S. forces.

The Chinese military will maintain high vigilance, resolutely defend sovereignty and maritime rights and interests, and resolutely safeguard peace and stability in the South China Sea, China’s military said.

“The Philippines enlisted forces out of the region to patrol … stirred up trouble and engaged in hype, undermining regional peace and stability,” the southern theatre command of the Chinese military said.

Philippine officials have said their military and the U.S. launched joint patrols on Tuesday in waters near Taiwan, a democratically governed island that China claims as its own, raising the possibility of further tensions with China.

Relations have soured between China and the Philippines over the South China Sea under Philippine President Ferdinand Marcos Jr as he pivots towards closer ties with the U.S., which supports the Southeast Asian nation in its maritime disputes with China.