Mattis accuses China of 'intimidation and coercion' in S. China Sea

China's military build-up in the South China Sea and its deployment of high-end weapons systems in the disputed waterway is designed to intimidate and coerce neighbours, US Defense Secretary Jim Mattis said today.

Speaking at a high-profile security summit in Singapore less than two weeks before President Donald Trump is due to meet North Korean leader Kim Jong Un, the Pentagon chief also said the US military continues to support diplomats pushing for the "complete, verifiable and irreversible" denuclearisation of the Korean peninsula.

Mattis said Beijing had deployed a range of military hardware including anti-ship missiles, surface-to-air missiles and electronic jammers across the South China Sea, where it has built islets and other maritime features into hardened military facilities.

Beijing has also landed heavy bombers on Woody Island in the Paracel Islands.

"Despite China's claims to the contrary, the placement of these weapon systems is tied directly to military use for the purposes of intimidation and coercion," Mattis told the Shangri-La Dialogue.

He also blasted Chinese President Xi Jinping for reneging on a 2015 promise made at the White House that Beijing would not militarise the island features in the South China Sea.

Mattis' address in Singapore was the second time he had attended the summit since becoming Pentagon chief.

He returned to a theme that he and other senior US officials have hammered since Trump took office -- that America is here to stay in the Asia-Pacific region and that allies should stick with Washington instead of aligning with Beijing.

But the message of inclusivity, cooperation and working with allies might be a tougher sell for Mattis, who is generally popular on the international scene, after his boss this week imposed metals tariffs on some of America's closest allies in the name of "national security". Washington Post columnist Josh Rogin asked Mattis whether he thought it was unproductive for Trump to pick fights with allies on trade.

"Certainly we have had some unusual approaches, I'll be candid with you," Mattis replied.

"But I'm reminded that so long as nations continue dialogue, so long as they continue to listen to one another and to pay respect to one another, nothing is over based on one decision."
"They believe that piling mountainous debts on their neighbours and somehow removing the freedom of political action is the way to engage them. Eventually these things do not pay off."