BEIJING • China yesterday said it was "extremely concerned" about a suggestion from a top US commander that US ships and aircraft should challenge China's claims in the South China Sea by patrolling close to artificial islands it has built.

The United States has accused China of reclaiming land in the disputed waters, and building ports and air facilities on several reefs in the Spratly Islands - often interpreted as an increasingly assertive action to back up China's sovereignty claims in the South China Sea.

The reclamation projects have rattled China's neighbours, in particular the Philippines, a close ally of the US, and raised concerns in the US.

Admiral Harry Harris, the commander of US forces in the Pacific, told a Senate hearing on Thursday that China's move to build three airfields on small islands in the South China Sea, and their further militarisation, was of "great concern, militarily", and posed a threat to all countries in the region.

Pressed by members of the Senate Armed Services Committee on whether US forces should challenge China by sailing within 12 nautical miles of the islands, Adm Harris said: "I believe we should exercise, be allowed to exercise, freedom of navigation and flight - maritime and flight - in the South China Sea against those islands that are not islands."

Asked if this meant going within 12 miles, he answered, referring to the artificial islands: "Depending on the feature." He added: "Conducting that kind of... freedom-of-navigation operation is one of the operations we're considering."

US Assistant Secretary of Defence David Shear told the committee that such patrols have not been conducted since 2012 but were among an "array" of future US options.

Chinese Foreign Ministry spokesman Hong Lei said on Friday China was "extremely concerned" about the comments and China opposed "any country challenging China's sovereignty and security, in the name of protecting freedom of navigation".

"We demand that the relevant country speak and act cautiously, earnestly respect China's sovereignty and security interests, and not take any risky or provocative acts," he said at a daily news briefing.

Mr Hong reiterated that China had strong historical evidence and legal support to justify its claims in the South China Sea.

Chinese President Xi Jinping is expected to demonstrate China's increasing global influence on his first state visit to the US next week for a closely watched summit with US President Barack Obama, even as concern builds that its giant economy is losing steam.

US concerns about China's pursuit of territorial claims in the South China Sea will be high on Mr Obama's agenda in their talks.

China has overlapping claims with Vietnam, the Philippines, Malaysia, Taiwan and Brunei in the South China Sea, through which US$5 trillion (S$7 trillion) in ship-borne trade passes every year.

Mr Xi on Thursday spoke of a "new model of major country relations" in a dialogue with US business leaders in Beijing.

The Chinese leader said he was ready to have a "profound exchange of views with President Obama on major issues of mutual concern".

Mr Ruan Zongze, vice-president of the China Institute of International Studies, a foreign ministry-affiliated think-tank, told diplomats at the Lanting forum in Beijing that the nature of the US-China relationship had changed.

"The world is entering a stage of major adjustments and changes," he said on Wednesday. "Under such circumstances, China cannot just remain silent like it was before."

Chinese officials see the summit as an opportunity to tone down worries in the US over its global ambitions and increasing military profile, along with accusations that Beijing has been behind major acts of cyber espionage against the US government and companies.

China has been playing "a bigger role in international relations", as urged by the US, Mr Ruan said, only to find Washington expressing concern when it did so.

"The crux of the problem lies in the zero-sum mentality in the United States because a lot of Americans see China as a source of problems as it grows stronger."

REUTERS, AGENCE FRANCE-PRESSE