InvestIdeas

“We’re going to have to send China a clear signal that first the island-building stops and second your access to those islands is also not going to be allowed,” he said when asked whether he would support a more aggressive posture in the South China Sea. He compared China’s actions to those of Russia in the Crimea.

China claims more than 80 percent of the South China Sea, where it has constructed artificial land features on seven rocks and reefs, and installed military facilities.

China might set up an air ­defence identification zone if the US tried to block China’s access to the islands

China would also retaliate if, as Tillerson also indicated, the US unilaterally upgraded punishment of Chinese companies violating UN sanctions against North Korea

“If China will not comply with the UN sanctions, then it’s appropriate ... for the United States to consider actions to compel them to comply”

Spicer declined to elaborate when asked how the United States could enforce such a move against China, except to say: "I think, as we develop further, we'll have more information on it."

Aides have said that Trump plans a major naval build-up in East Asia to counter China's rise.

“What we have to do is exhaust all efforts, diplomatic efforts, to try to resolve this properly, maintaining open lines of communication,” Mattis said, in his most complete remarks on the issue to date.

“And certainly our military stance should be one that reinforces our diplomats in this regard. But there is no need right now at this time for military maneuvers or something like that, that would solve something that’s best solved by the diplomats.”

“China has shredded the trust of nations in the region, apparently trying to have a veto authority over the diplomatic and security and economic conditions of neighboring states,” he said.

The United States is putting regional stability in East Asia at risk, a Chinese spokesman said on Saturday following remarks by the new US Defence Secretary Jim Mattis that a US commitment to defend Japanese territory applied to an island group claimed by China

So how would Secretary Tillerson justify a blockade? No US allies or partners – Japan, Singapore or India – have shown the slightest interest in joining in. It would arguably be a breach of international law and very likely to be viewed by China as an act of war.

As for China, there are competing strands at work in its foreign policy. Its behaviour oscillates between rising-power forcefulness and cautious diplomacy. But with all of Southeast Asia engaging with it, Beijing would lose a lot by returning to assertiveness. In a sense, it is locked into restraint by its recent diplomacy.

The Asia Maritime Transparency Initiative at the Centre for Strategic and International ­Studies in Washington said on Wednesday that China now ­occupied 20 outposts in the ­Paracels, and that there had been an extensive military build-up on eight islands.

“Three of these now have ­protected harbours capable of hosting large numbers of naval and civilian vessels. Four others boast smaller harbours, with a fifth under construction at Drummond Island,” the group said on its website.

“Five of the islands contain helipads, with Duncan Island housing a full helicopter base. And the largest of the Paracels, Woody Island, sports an airstrip, hangars and a [detachment] of HQ-9 surface-to-air missile batteries.”

The official, speaking on condition of anonymity, said the aircraft came within 1,000 feet (305 meters) of each other on Wednesday in the vicinity of the Scarborough Shoal, between the Philippines and the Chinese mainland.