US Defense Secretary Jim Mattis said that Chinese actions in South China Sea call into question China's broader goals.

James Mattis said China's actions in the region stood in "stark contrast" to the United States policy of openness and called into question China's goals.

"The placement of these weapon systems is tied directly to military use for the objective of intimidation and coercion", Mattis said, adding, "China's militarization of the Spratlys is also in direct contradiction to President Xi Jinping's 2015 public assurances in the White House Rose Garden that they would not do this". Beijing has repeatedly warned the United States against sending warships to patrol the South China Sea.

Mattis said on Friday that the US would continue to "pursue a constructive, results-oriented relationship with China".

Speaking at a high-profile security summit in Singapore 10 days before President Donald Trump is due to meet North Korean leader Kim Jong Un, the Pentagon chief also said the USA military continues to support diplomats pushing for the "complete, verifiable and irreversible" denuclearization of the Korean peninsula (see story on D1).

Two US warships sailed close to the Paracel Islands on May 27 in the latest freedom of navigation operation created to challenge Beijing's claims.

Mr Mattis's comments drew a pointed reaction from a Chinese official at the meeting.

Satellite images of the Hughes and Gaven reefs also showed what appeared to be anti-aircraft guns and what were likely to be close-in weapons systems (CIWS) to protect against cruise missile strikes.

Woody Island, which China calls Yongxing, is also claimed by Vietnam and Taiwan.

The United States has once again accused China of militarizing the South China Sea to intimidate and coerce neighbors.

The Chinese government and the Chinese people resolutely oppose U.S. arms sales to Taiwan as well as any official contact with Taiwan and upgrading ties with Taiwan in any way, said He Lei, vice president of the Academy of Military Science of the Chinese People's Liberation Army.

China believes islands, islets and other maritime features in the South China Sea are its sovereign territory and that it is within its rights to build defenses on them.

He added there would be "consequences" if China does "not find the way to work more collaboratively with all of the nations who have interest".

Speaking at an global security forum in Singapore, Mr Mattis rebuked China's military build-up in the disputed waters, warning of increasingly severe consequences should the rising Asian power fail to work collaboratively with neighbouring countries.

As expected, the Pentagon chief gave only a brief mention of the ongoing negotiations for an historic summit later this month between President Trump and North Korean leader Kim Jong Un.

Mattis also sought to calm nervous allies in the region.

He added that the status of USA troops in South Korea was not on the table when Mr Trump and Mr Kim meet, but left the door open to the issue being discussed down the road between Seoul and Washington if certain conditions were met.

Mattis said the Pentagon will "hold the line" and support the diplomatic effort to secure the "complete, verifiable, and irreversible denuclearization of the Korean Peninsula".