The Philippines will hold joint naval drills with the United States, Japan and Australia, two diplomatic sources told AFP Thursday, as the four countries deepen military ties to counter China's expanding influence in the Asia-Pacific region.

The exercise will be held Sunday in the disputed South China Sea -- which Beijing claims almost entirely -- days before US President Joe Biden is due to hold the first trilateral summit with the leaders of the Philippines and Japan.

The diplomatic sources spoke on condition of anonymity because the drills have not yet been officially announced.

Earlier this week, the Australian warship HMAS Warramunga arrived at the Philippine island province of Palawan, which faces the hotly contested waters.

The Philippine military said the visit was "aimed at strengthening military relations with partner nations".

Regional tensions have escalated in the past year as China becomes increasingly confident in asserting its claims over waters also claimed by the Philippines and Japan, as well as over self-ruled Taiwan.

In response, the United States has sought to strengthen its alliances in the region, including with treaty allies Japan and the Philippines.

Biden's planned April 11 summit with Philippine President Ferdinand Marcos and Japanese Prime Minister Fumio Kishida at the White House will be the latest in a series of meetings with Asia-Pacific partners.

Biden will also hold separate bilateral meetings with Marcos and Kishida.

Joint patrols between the US, Japanese and Philippine coast guards are expected to be announced during the summit, one of the diplomatic sources told AFP, after joint drills were held for the first time last year.

- 'Ironclad' -


The exercise and summit follow repeated confrontations between Chinese and Philippine vessels near disputed reefs off the Southeast Asian country in recent months.

Top US officials have repeatedly declared the United States' "ironclad" commitment to defending the Philippines against an armed attack in the South China Sea.

Relations between Manila and Beijing have deteriorated under Marcos, who has taken a stronger stance than his predecessor Rodrigo Duterte against Chinese actions in the sea.

China claims most of the waterway, through which trillions of dollars worth of trade passes annually, despite rival claims from other nations and an international ruling that its claim has no legal basis.

Marcos issued a strongly worded statement on March 28, vowing the Philippines would not be "cowed into silence, submission, or subservience" by China.

He also said the Philippines would respond to recent incidents with countermeasures that would be "proportionate, deliberate, and reasonable".

Meanwhile, talks between the Philippines and Japan for a defence pact that would allow the countries to deploy troops on each other's territory were "still ongoing", a spokesman for the Philippine foreign affairs department told reporters Thursday.

Manila already has a similar agreement with Australia and the United States.