China on Sunday test-landed a plane on an airstrip it constructed on the disputed Spratly Islands, inviting a furious response from Vietnam and expression of concern from Washington, ratcheting up tension in the already hot South China Sea.
Japan and the Philippines lend support to Vietnam's expression of anger at Beijing after a Chinese plane landed on an airstrip it constructed on the islands, which have been artificially enlarged by China.
China, which is defiant against all criticism and continues to claim almost the entire South China Sea as its backyard, has been causing alarm among its neighbours as it builds up infrastructure on reefs in the disputed waters.
The flight at Fiery Cross Reef in the Spratly Islands "adds to tension and uncertainties in the region," Charles Jose, a spokesman for Philippines' department of foreign affairs, said on Monday.
Japanese foreign minister Fumio Kishida told media that the flight was an attempt by China to make its island-building ''a fait accompli,'' according to Japan's Kyodo news agency.
''Japan is gravely concerned about China's act, which is a unilateral change of the status quo,'' Kishida said.
China has become increasingly assertive over its territorial claims in recent years and has been ramping up military spending.
Some observers say the airstrips being built in the South China Sea are capable of hosting military jets.
Hanoi had protested at the flight, labelling it "a serious infringement of the sovereignty of Vietnam.''
"We did not find this particular flight activity to be helpful to security and stability in the region; that it runs counter to our belief that the reclamation process needs to stop; that the militarisation of facilities, whether they are reclaimed or not, in the region should stop, because it's just increasing tension,'' US state department spokesman John Kirby told reporters at his daily news conference yesterday.
''Our concern is that to begin flight operations at a new airfield in a disputed area is only going to raise tensions and threaten regional stability,'' he said.
John McCain, the chairman of the US Senate Armed Services Committee, said the Obama administration was allowing China to continue to "pursue its territorial ambitions" by delaying ''freedom of navigation'' patrols near the islands.
China has confirmed that a test flight by a civilian plane landed on an artificial island built in the Spratlys, the first time Beijing has used a runway in the area.
Beijing, however, denied the island building is aimed at boosting its military might, and Hua Chunying, foreign ministry spokeswoman, reiterated China's position that it had ''indisputable sovereignty'' to the Spratlys, which are called the Nansha Islands in China.
Malaysia, Brunei, and Taiwan also have rival claims to islands in the disputed waters.
The spokeswoman also said a civil aircraft was used to conduct the test, and that China hoped it could continue ''sustainable, healthy and stable'' ties with Vietnam.
More than $5 trillion (£1.95 million) of world trade passes every year through the South China Sea, which is also said to hold huge deposits of gas.