The declaration of the ADIZ, which could potentially interfere in normal flight operations and freedom of navigation and over-flights, was highly provocative, said Colin Willett, US deputy assistant secretary of state for East Asian and Pacific affairs, “and I think it is not acceptable to anyone in the international community”.

Chinese Vice Foreign Minister Liu Zhenmin said earlier that Beijing could set up an air-defence zone over the South China Sea if it felt threatened after the Permanent Court of Arbitration (PCA) at The Hague ruled in favour of the Philippines in the legal battle over the contentious sea.

“The declaration of such a zone, which would require aircraft entering the zone to identify themselves to the military, will depend on the level of threat we receive,” Liu was quoted as saying by China Daily.

China took a similar action in 2013 when Beijing was in conflict with Tokyo over the Diaoyu/Senkaku Islands in the East China Sea.

Speaking via telephone from Washington with journalists in Southeast Asia yesterday, Willett urged countries in the region to refrain from provocative behaviour or using force to respond to the situation.

Asking if a joint exercise on maritime law enforcement between the Philippines and Japan this week could also be considered as “provocative action”, Willett said such exercises in line with international law were not considered provocative.

‘Rights of nations’

 “The main focus is to ensure that everyone has behaviour which is consistent with international law, [protects] the right of all nations to exercise freedom of navigation and over-flight, and doesn’t raise tensions or do something destabilising or dangerous,” she said.

The PCA ruled on Tuesday in favour of Manila on four key elements.

The court found there were no historical grounds for China’s “nine-dash line”, which stakes a claim to a huge area in the South China Sea.

It also said features named in the submission by the Philippines were entitled to sovereign territory beyond 12 nautical miles, Beijing’s construction of artificial islands and interference with fishing vessels violated the Philippines’ rights, and China’s large land reclamations and fishing activities damaged the environment.

While Beijing said it did not recognise or accept the court judgement, Willett said both China and the Philippines were parties to the 1982 United Nations Convention on the Law of the Sea and had an obligation to comply with the ruling.

The US official said the international community also had an obligation to support the court’s decision and urged all parties to comply.

“The international community has the obligation to ensure peace and stability in the region, and ensure that the rule-based order is upheld,” Willett said.