Manila has rejected Beijing's demand that it "disregard" an international ruling that invalidated the Asian giant's claims to much of the South China Sea before negotiating on the issue, the Philippines' foreign secretary said Tuesday.

China last week denounced a UN-backed tribunal's finding that there was no legal basis for its claims to most of the strategic, resource-rich waters, provoking stern warnings from leaders from Japan to the EU that it must respect the rule-based global order.

Following the decision, Beijing asked Manila, which brought the case, "to open ourselves for bilateral negotiations but outside of and in disregard of the arbitral ruling", foreign minister Perfecto Yasay told broadcaster ABS-CBN.

"This is something that I told him was not consistent with our constitution and our national interest," he said.

The Hague-based Permanent Court of Arbitration (PCA) ruled that Beijing had violated the Philippines' sovereign rights to exploit resources in waters up to 340 kilometres (230 miles) beyond its coast, called its exclusive economic zone.

It said there was no legal basis to China's claims to much of the sea, embodied in a "nine-dash line" dating from 1940s maps.

Yasay's comments were more forceful than previous Philippine reactions, with Manila's new President Rodrigo Duterte keen to restore relations with Beijing and promising not to "taunt or flaunt" the verdict.

Many other countries have been more outspoken.

At an Asia-Europe summit in Mongolia at the weekend, Japanese Prime Minister Shinzo Abe and European Union President Donald Tusk took China to task for its refusal to respect the decision.

China has long denied the tribunal's authority to rule on the case, calling it a "fraud" and accusing its members of accepting money from Manila.

Yasay and his Chinese counterpart Wang Yi discussed the possibility of talks on the sidelines of the Ulan Bator summit but made no headway, he said, quoting Wang as telling him: "If you will insist on the ruling, discussing along those lines, then we might be headed for a confrontation."

Direct talks were unlikely soon in the light of Beijing's refusal to accept the ruling, Yasay said.

- 'Let the dust settle' -

On Tuesday, China launched war games in waters some distance north of the contested area.

Beijing has built a series of artificial islands in the sea capable of supporting military operations, and a top Chinese military official told a visiting US admiral this week that it would "never stop our construction" prematurely.

The project has raised concerns that Beijing may seek to hamper the free movement of ships and aircraft through the region, and may even create an air defence identification zone over the sea, which would seek to put restrictions on foreign planes.

A combat air patrol was mounted over the sea recently and they will become a regular practise in future, an air force spokesman said separately according to the official news agency Xinhua.

China seized Scarborough Shoal -- known as Huangyan Dao in Chinese -- in 2012 after a brief stand-off with the Philippine navy. Manila lodged suit at the tribunal the following year.

Beijing, which justifies its extensive claims by saying it was the first to have discovered, named and exploited the sea, has said the tribunal ruling cannot be the basis of any discussions.

Duterte's "first and foremost" priority was to regain access to Scarborough Shoal for Filipino fishermen, Yasay said.

The new president said last week that he would send former president Fidel Ramos to China to start talks on the ruling, but Yasay did not know if Ramos would accept and did not know when that mission could be dispatched.

"Let the dust settle some more and let's see how we can open up the road for this kind of negotiation," Yasay added.

In the long term, he said, Manila had not ruled out the possibility of giving China a role as a contractor when the government moves to exploit the resources, including natural gas, in its exclusive economic zone.