The Philippines has urged Beijing to respect an international tribunal's ruling that rejected Chinese claims to most of the South China Sea, while a former United States naval chief has said the US should be willing to use military force to oppose Chinese aggression in the region.

A statement from the Philippines' Foreign Affairs Department said Foreign Secretary Perfecto Yasay would also discuss the ruling with China at the two-day Asia-Europe summit, known as Asem, starting today in Mongolia. Chinese Premier Li Keqiang will be at the summit.

Meanwhile, Dennis Blair, a former commander of US forces in the Pacific, told a congressional hearing that the US should not pick a fight with China at the disputed Scarborough Shoal off the coast of the Philippines, but set a limit on its military coercion.

"I think we need to have some specific lines and then encourage China to compromise on some of its objectives," he told a Senate hearing.

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The Philippines is a US ally, but their treaty is ambiguous about whether the US would come to its defence in disputed territory.

A 2012 standoff at Scarborough Shoal between Chinese and the Philippine vessels prompted Manila to launch the arbitration case by the Permanent Court of Arbitration in The Hague.

The statement from the Philippines' Foreign Affairs Department said: "Secretary Yasay will discuss within the context of Asem's agenda the Philippines' peaceful and rules-based approach on the South China Sea and the need for parties to respect the recent decision."

The statement was the strongest response from the Philippines to Tuesday's verdict which declared that China's claims to the resource-rich and strategically vital South China Sea had no legal basis.

China vowed to ignore the ruling, saying the United Nations-backed tribunal had no jurisdiction over the case and accused it of bias.

China on Wednesday also raised the prospect of confrontation in the sea, and threatened to introduce an air defence zone over the sea that would give its military authority over foreign aircraft.

China said on Monday that the maritime dispute should not be included on the Asem agenda, with Assistant Foreign Minister Kong Xuanyou insisting the meeting was "not an appropriate venue" to discuss the issue.

The Asem summit brings together nations from Asia and Europe, including other sea claimants Vietnam and Malaysia.

In his first comments immediately after the ruling, Yasay said the Philippines welcomed the decision but he did not urge China to respect or abide by it.

Yasay will be at Asem representing President Rodrigo Duterte, who has signalled he wants to avoid a major diplomatic falling-out with China over the issue.

China claims nearly all of the South China Sea, even waters approaching the coasts of the Philippines and other Southeast Asian nations.

China justifies its claims by saying it was the first to have discovered, named and exploited the sea, and outlines its claims for most of the waterway using a vague map made up of nine dashes that emerged in the 1940s.

The tribunal ruled China's claimed historical rights and nine-dash map had no legal basis.

- AFP, AP