The US called on China on Saturday to cease harassing Philippine ships in the South China Sea, promising to stand behind the Philippines at a time of boiling geopolitical tension.

“We call on Beijing to cease its provocative and dangerous behavior,” the US State Department said in a statement.

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

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.”