Updated June 03, 2017 15:24:22

The United States is encouraged by Beijing's efforts to restrain North Korea but Washington will not accept its militarisation of islands in the South China Sea, US Defence Secretary Jim Mattis says.

The comments by Mr Mattis, during the annual Shangri-La Dialogue forum, show how US President Donald Trump's administration is looking to balance working with China to restrain North Korea's advancing missile and nuclear programs while dealing with Beijing's activities in the South China Sea.

Mr Trump has actively courted support from Chinese President Xi Jinping to restrain North Korea, raising concern among Asian allies that Washington might allow China a more free rein elsewhere in the region.

Mr Mattis said the threat from North Korea was "clear and present" and that Pyongyang had increased its pace of pursuing nuclear weapons.

The United States has struggled to slow North Korea's nuclear and missile programs, which have become a security priority given Pyongyang's vow to develop a nuclear-tipped missile capable of hitting the US mainland.

The Trump administration has been pressing China aggressively to rein in its reclusive neighbour, warning all options are on the table if North Korea persists with its weapons programs.

"The Trump administration is encouraged by China's renewed commitment to work with the international community toward denuclearisation," Mr Mattis said.

"Ultimately, we believe China will come to recognise North Korea as a strategic liability, not an asset."

The United States would work with countries in the region to put new diplomatic and economic pressure on North Korea, he added.

The UN Security Council has expanded targeted sanctions against Pyongyang after its repeated missile tests, adopting the first such resolution agreed by the United States and China since Trump took office.

In another sign of increased pressure on North Korea, Japan's navy and air force began a three-day military exercise with two US aircraft carriers in the Sea of Japan on Thursday.

Photo: Japan Air Self-Defence Force F-15 fighter jets fly over US Navy aircraft carrier USS Carl Vinson in the Sea of Japan. (AP: Japan Air Self-Defence Force)

Countries 'must contribute sufficiently to their own security'

Allies around the world have been concerned about the commitment of the United States since Mr Trump took office because of his "America First" rhetoric and expectations that he would concentrate on a domestic agenda.

Mr Mattis sought to ease concerns for allies in the Asia Pacific, saying the region was a priority and the primary effort was alliance building. He added, however, that countries must "contribute sufficiently to their own security".

He also said the US alliance with Australia remained relevant in the 21st century and praised Mr Turnbull for a major speech in which he criticised China's aggression in the South China Sea.

Mr Mattis said the United States welcomed China's economic development, but he anticipated "friction" between the two countries.

"While competition between the US and China, the world's two largest economies, is bound to occur, conflict is not inevitable," Mr Mattis said.

While eager to work with China in dealing with North Korea, Mr Mattis said the United States did not accept China placing weapons and other military assets on man-made islands in the South China Sea.

"We oppose countries militarising artificial islands and enforcing excessive maritime claims," Mr Mattis said. "We cannot and will not accept unilateral, coercive changes to the status quo."

China's claims in the South China Sea, through which about $5 trillion in ship-borne trade passes each year, are contested by Brunei, Malaysia, the Philippines, Taiwan and Vietnam.

Reuters

Topics: world-politics, unrest-conflict-and-war, united-states, korea-democratic-people-s-republic-of, china, singapore

First posted June 03, 2017 13:07:19