U.S. Assistant Secretary of State for East Asia and Pacific Affairs Daniel Kritenbrink on Saturday said the situation in the South China Sea is deeply concerning, and said China's recent actions in the disputed waterway were "deeply destabilising", Paralel.Az reports citing Reuters.

Kritenbrink made the comments during a visit to Hanoi, amid rising tension between China and the Philippines in the South China Sea, where Vietnam is also a claimant.

"We think that China's actions, particularly its recent actions, around the Second Thomas Shoal, vis-à-vis the Philippines have been irresponsible, aggressive, dangerous, deeply destabilising," Kritenbrink said at a briefing for selected media in Hanoi, a recording of which was reviewed by Reuters.

"We're going to continue to stand with our Filipino allies," Kritenbrink said, adding that Washington had made it clear, both publicly and privately, to Beijing that the mutual defence treaty obligations it has with the Philippines were "ironclad".

On Friday, Philippine officials said they did not consider invoking the mutual defence treaty with the U.S. after accusing China of aggressively disrupting a resupply mission in the disputed South China Sea earlier this month.

China's foreign ministry disputed the Philippines' account, with a spokesperson saying on Thursday that the necessary measures taken were lawful, professional and beyond reproach.

"We think every country in the region, including China, needs to respect international law and needs to behave responsibly in the maritime domain," Kritenbrink said.

China claims almost the entire South China Sea, a conduit for more than $3 trillion of annual shipborne commerce, including parts claimed by the Philippines, Vietnam, Indonesia, Malaysia and Brunei.

In 2016, the Permanent Court of Arbitration in The Hague said China's claims had no legal basis, a decision Beijing has rejected.

Kritenbrink arrived in Hanoi on Friday on the heels of a visit to Vietnam by Russian President Vladimir Putin that was sharply criticised by Washington.

"Only Vietnam can decide how best to safeguard its sovereignty and advance its interests," Kritenbrink said when asked about his view on Vietnam's foreign policy and its hosting of Putin.

Vietnam and the U.S. officially upgraded their relationship to a comprehensive strategic partnership, Vietnam's highest tier of its diplomatic ranking, during a visit to Hanoi by President Joe Biden in September last year.

Kritenbrink said upgrade was "historic and momentous", and said he wanted to maintain momentum to make sure that all of the agreements reached are implemented.

"We continue to believe that the U.S.-Vietnam partnership has never been stronger," he said.