In a time of simmering geopolitical tension, the United States on Saturday urged China to stop harassing Philippine ships in the South China Sea and vowed to support the Philippines.

The United States State Department issued a statement saying, “We call upon Beijing to desist from its provocative and unsafe conduct.”

The Philippines on Friday accused China’s coast guard of “aggressive tactics” following an incident during a Philippine coast guard patrol close to the Philippines-held Second Thomas Shoal, a flashpoint for previous altercations located 105 nautical miles (195 km) off its coast.

The Second Thomas Shoal is home to a small military contingent aboard a rusty World War Two-era U.S. ship that was intentionally grounded in 1999 to reinforce the Philippines’ territorial claims. In February, the Philippines said a Chinese ship had directed a “military-grade laser” at one of its resupply vessels.

China claims sovereignty over almost the entire South China Sea with a “nine-dash line” on maps that stretches more than 1,500 km off its mainland and cuts into the exclusive economic zones of Vietnam, the Philippines, Malaysia, Brunei and Indonesia. An international arbitral ruling in 2016 dismissed that line as having no legal basis.

China’s foreign ministry on Friday said the Philippine vessels had intruded into Chinese waters and made deliberate provocative moves.

The State Department said Washington “stands with our Philippine allies in upholding the rules-based international maritime order.”