Security engagements between the treaty allies have soared in the past year, at a time of tension in the South China Sea, where the Philippines and China have traded blame over a spate of run-ins over territory.

It was the third time the Philippines and former colonial ruler the US have held joint exercises in the South China Sea since November last year, moves that have frustrated Beijing, which objects to what it sees as US interference in its backyard.

“It demonstrates our commitment to a free and open Indo-Pacific, and foster close cooperation towards further enhancing our maritime capabilities,” Armed Forces of the Philippines chief Romeo Brawner said in a statement.

China claims sovereignty over almost the entire South China Sea, a conduit for more than US$3 trillion of commercial shipping annually, including parts of the exclusive economic zones of the Philippines, Vietnam, Indonesia, Malaysia, and Brunei.

It has policed those claims with a vast coastguard fleet that the Philippines has accused of hostile intentions and actions that are against international law. China says it is protecting its territory.