The US on Thursday disclosed for the first time that American ships have started conducting joint patrols with the Philippines in the South China Sea, a somewhat rare move not done with many other partners in the region. At the same time, Defence Secretary Ash Carter announced at a joint news conference with Philippine Defense Secretary Voltaire Gazmi that the United States will be keeping nearly 300 troops, including Air Force commandos armed with combat aircraft and helicopters, in the Philippines through the end of the month.

It’s part of a military build-up sure to inflame tensions with Beijing in the South China Sea. The US will also begin sending forces on increased rotations into the Philippines, it was disclosed, to beef up training and to support increased military operations in the region.

The increase in military support comes just days after a Philippine diplomat asked that the US help convince China not to build in the nearby Scarborough Shoal, which is viewed as important to Filipino fishermen.

Philippine Ambassador to Washington Jose Cuisia Jr said the Philippines is not capable of stopping China from constructing there. China has built man-made islands in other contested spots in the South China Sea.

According to the Pentagon, the US forces that will remain here are already in the Philippines participating in the Balikatan or shoulder-to-shoulder combat exercises which will end tomorrow.

About 200 airmen, including special operations forces will remain at Clark Air Base, along with three of their Pave Hawk attack helicopters, an MC-130H Combat Talon II special mission aircraft and five A-10 combat aircraft.

This initial contingent will provide training to increase the two militaries’ ability to work together, laying the groundwork for forces to do joint air patrols as well as the ship movements. Also, up to 75 Marines will stay at Camp Aguinaldo to support increased US and Philippine combined military operations in the region.

The troops and aircraft are expected to leave at the end of the month, but other US forces and aircraft would do similar rotations into the Philippines in the future. A defence official would not say how frequently those rotations would happen, but said the size schedule and makeup would fluctuate. The official was not authorized to discuss the issue publicly so spoke on condition of anonymity.