President Ferdinand Marcos said on Sunday the Philippines “will not be intimidated” by anyone after a violent clash between the Filipino navy and the Chinese coast guard in the South China Sea.

The confrontation took place on Monday off Second Thomas Shoal as Chinese sailors foiled an attempt by Philippine forces to resupply marines stationed on a derelict warship that was deliberately grounded atop the disputed shoal in 1999 to assert Manila’s territorial claims.

It was the latest and most serious incident in a series of escalating confrontations between Chinese and Philippine ships in recent months as Beijing steps up efforts to push its claims to nearly all of the strategically located waterway.

“We will never be intimidated or oppressed by anyone,” Marcos said in a speech during a visit to the headquarters of the Philippines’ South China Sea forces on Palawan island, the closest major landmass to the shoal.

Marcos awarded medals to 80 sailors who took part in the resupply mission, urging them to “continue to fulfil your duty of defending the nation” even as the situation has become “dangerous”.

Second Thomas Shoal lies about 200 kilometres from Palawan and more than 1,000 kilometres from China’s nearest major landmass, Hainan island.

A Filipino sailor lost a thumb in the clash with Manila also accusing the Chinese coast guard sailors of wielding knives, sticks and an axe and stealing or damaging their equipment, including guns and inflatable boats.

Beijing insisted its coast guard behaved in a “professional and restrained” way and blamed Manila for the clash.

In previous confrontations, Chinese forces have used water cannons and military-grade lasers and collided with Filipino resupply vessels and their escorts.

“We have never, never in the history of the Philippines, yielded to any foreign power,” Marcos said to applause, while pledging to “continue to exercise our freedoms and rights in support of our national interest, in accordance with international law”.

“Our calm and peaceful disposition should not be mistaken for acquiescence.”

The confrontation is fuelling growing concern that the dispute could drag in the United States, which has a mutual defence pact with Manila.

The Philippine government said this week that it does not consider Monday’s clash as an “armed attack” that would trigger a provision in the treaty for Washington to come to Manila’s aid.

However, Manila says it was also concerned Chinese forces would launch a similar attempt to dislodge a small Filipino military garrison on Second Thomas Shoal.