The Philippines yesterday accused China’s coast guard of blocking and water-cannoning a Philippine military supply boat in the South China Sea, condemning the “excessive and offensive actions” against its vessels.

China’s coast guard countered that it had implemented necessary controls in accordance with the law to deter Philippine ships, which it accused of trespassing and carrying illegal building materials.

After the incident, the US State Department said China’s “repeated threats to the status quo in the South China Sea (were) directly threatening regional peace and stability” and that Washington stands with its Philippine allies in the face of such “dangerous actions”.

“The United States reaffirms an armed attack on Philippine public vessels, aircraft, and armed forces – including those of its Coast Guard in the South China Sea – would invoke US mutual defense commitments under Article IV of the 1951 US Philippines Mutual Defense Treaty,” it said in a statement.

China claims sovereignty over almost the entire South China Sea, an assertion rejected internationally, while Malaysia, Vietnam, Brunei, Taiwan, and the Philippines have various claims to certain areas.

Beijing often irks its neighbours with maritime actions they call aggressive and with longer-term activities like building islands on reefs and equipping them with missiles and runways.

A Chinese coast guard vessel on Saturday blocked and water-cannoned the chartered Philippine boat on a routine troop rotation and resupply mission, “in wanton disregard of the safety of the people on board and in violation of international law”, the Armed Forces of the Philippines said.

It said in a statement the incident occurred near the Second Thomas Shoal, which Manila calls Ayungin Shoal, a submerged reef where a handful of its troops live on a rusty World War Two-era US ship that was intentionally grounded in 1999.

The Chinese coast guard’s “dangerous manoeuvres” prevented a second boat from unloading the supplies and completing the mission, it said.

“We call on the China Coast Guard and the Central Military Commission to act with prudence and be responsible in their actions to prevent miscalculations and accidents that will endanger people’s lives,” the armed forces said.

China Coast Guard spokesman Gan Yu responded that China has “indisputable” sovereignty over the Spratly Islands and their adjacent waters, including the Second Thomas Shoal.

“We urge the Philippine side to immediately stop its infringing activities in these waters,” Gan posted on the coast guard’s WeChat social media account.