The United States and its friends can act to show China that the consequences of its actions in the South China Sea are far more damaging to itself than to other countries, US Senator John McCain said yesterday.

One of the moves they can make, he said, is to accelerate the ratification of the Trans-Pacific Partnership (TPP) - a free trade deal that brings together 12 nations, including the US, Japan and four Asean states.

"That would make for long-term economic benefits to every nation in the region engaged in it," he said at his lecture, America's Enduring Commitment To Security And Prosperity In Asia, organised by the S. Rajaratnam School of International Studies.

The senator, who chairs the US Senate Armed Services Committee, was replying to a question on how the US and countries in the region can respond should China reject the ruling of the Permanent Court of Arbitration (PCA) on a case against its claims to the South China Sea brought by the Philippines.

But he acknowledged that the TPP, signed earlier this year, faces stiff challenges. It looks unlikely to be approved by the US Congress any time soon, with candidates of the year-end presidential election opposed to the deal. "I have to give you the honest answer. Things are not good right now," he said.

The senator also suggested stepping up "freedom of navigation" operations to drive home the point that the South China Sea is international and "filling in islands is in violation of international law".

The latter refers to China's reclamation of islands on disputed reefs to bolster its overlapping claims in the waters with four Asean states.

American ships have sailed close to those islands to challenge China's claims.

On the PCA ruling, expected in the coming weeks, Mr McCain said its legitimacy "will be derived from the actions of nations that are not party to the case, especially those in South-east Asia".

He said the US will remain committed to regional security, continuing to "maintain a favourable military balance" in the region to safeguard open seas and open commerce, among other things.