China’s military has warned the Philippines against any provocations in the tense South China Sea as it continues to launch patrols and advance plans to solidify its control of the area.

A spokesperson for the Chinese military’s Southern Theater Command issued a statement directed at the Philippines that referenced joint drills with the United States and Japan in the major waterway carrying more than $3 trillion of annual commerce.

“We sternly warn the Philippine side to immediately stop provoking incidents and escalating tensions in the South China Sea, as well as bringing in external forces for backing such efforts that are destined to be futile,” the spokesperson said.

“Any attempt to stir up trouble or disrupt the situation will not succeed.”

Philippine maritime and military authorities have not commented immediately.

The warning comes after the US Asia Pacific Command said in a statement that Japan, the Philippines and the US conducted joint maritime exercises in the Philippine Exclusive Economic Zone from Thursday to Saturday to strengthen regional cooperation and support a free and open Asia Pacific region.

“The US, along with our allies and partners, upholds the right to freedom of navigation and overflight and other lawful uses of the sea and international airspace, as well as respect to the maritime rights under international law,” it said.

This comes days after China’s State Council on Wednesday revealed its intention to establish a nature reserve spanning 3,500 hectares (8,650 acres) on the disputed islet of Scarborough Shoal, a contested territory claimed by both China and the Philippines in the South China Sea.

The Philippines strongly protested the move, and was backed by a statement of condemnation issued by US Secretary of State Marco Rubio on Friday.

“This is yet another coercive attempt to advance China’s interests at the expense of its neighbours and regional stability,” Rubio said, adding that Beijing was trying to “push expansive maritime and territorial claims”.