By Neil Jerome Morales

MANILA - The Philippines will implement countermeasures proportionate and reasonable against "illegal, coercive, aggressive, and dangerous attacks" by China's coastguard and maritime militia in the South China Sea, President Ferdinand Marcos Jr. said on Thursday.

"We seek no conflict with any nation, more so nations that purport and claim to be our friends but we will not be cowed into silence, submission, or subservience," Marcos said on Facebook.

He did not specify what the countermeasures would include.

The Philippines has been furious in the past year over what it calls repeated aggression by China's coastguard and allied fishing vessels around disputed features located inside Manila's 200-mile exclusive economic zone.

The latest flare-up occurred last week, when China used water cannon to disrupt another Philippine resupply mission to the Second Thomas Shoal for soldiers posted to guard a warship intentionally grounded on a reef 25 years ago.

China, which claims almost the entire South China Sea as its own, has accused the Philippines of encroaching on its territory and says it took necessary measures against the vessels.

China warned the Philippines on Monday to behave cautiously and seek dialogue, saying their relations were at a "crossroads" as confrontations between their coastguards over maritime claims worsened tensions.

Marcos said he met his defence and security officials and has been in communication with "friends in the international community".

"They have offered to help us on what the Philippines requires to protect and secure our sovereignty, sovereign rights, and jurisdiction while ensuring peace and stability in the Indo-Pacific," Marcos said.

The deterioration in relations with China come at a time when Marcos seeks to deepen defence ties with the United States. He has increased U.S. access to Philippine military bases and joint exercises have been expanded to include sea and air patrols over the South China Sea, vexing Beijing.

U.S. Defense Secretary Lloyd Austin on Wednesday reaffirmed Washington's commitment to a 1951 mutual defense treaty with the Philippines and criticised as "dangerous" China's actions at the Second Thomas Shoal.

In a phone call on Wednesday with his Philippine counterpart Gilberto Teodoro, Austin "reaffirmed the ironclad U.S. commitment to the Philippines" which it said was undertaking a lawful resupply mission.

The Philippine-U.S. treaty binds both countries to defend each other if under attack and includes coastguard, civilian and military vessels in the South China Sea.