US Defence Secretary Jim Mattis said on Friday the United States remains committed to its Asia-Pacific allies, as he arrived in Singapore for the region's premier defence and security forum.
Mattis, who is making his second visit to the region since he took charge of the Pentagon on Jan. 20, will be looking to articulate a clear US policy for allies in the region and reassuring them.
Trump has actively courted Chinese support on North Korea, raising concerns among Southeast Asian allies in the lead-up to the dialogue that Washington might allow China a freer rein elsewhere in the region.
Mattis told reporters that in a speech on Saturday to the annual Shangri-La Dialogue in Singapore he would talk about the "international order" needed for a peaceful Asia, a reference to countering North Korea's nuclear and missile programme.
"At the Shangri-la dialogue I will emphasise the United States stands with our Asia-Pacific allies and partners," Mattis told reporters on the way to the regional security forum.
"The Department of Defence is focused on strengthening alliances, empowering countries to be able to sustain their own security, and strengthening US military capabilities to deter war," Mattis said.
He is expected to meet with his counterparts from a number of countries including South Korea, Japan and Australia. China's delegation is led by a retired major-general from the Academy of Military Science, according to the forum's programme.
The US focus on North Korea has been sharpened by dozens of North Korean missile launches - the most recent of which was on Monday - and two nuclear bomb tests since the beginning of last year. Pyongyang has vowed to develop a nuclear-tipped intercontinental ballistic missile (ICBM) capable of hitting the US mainland.
Japan's navy and air force began a three-day military exercise with two US aircraft carriers in the Sea of Japan on Thursday adding pressure on North Korea to halt an accelerating ballistic missile programme.
US officials insist the administration remains committed more broadly to the region, much like it was under former President Barack Obama's administration.
Trump is due to attend regional summits in Vietnam and the Philippines in November.
The Pentagon also says it supports "in principle" a proposal by Senator John McCain, the head of the US Senate's Armed Services Committee, to increase military funding for the Asia-Pacific by US$7.5 billion (S$10.4 billion).
CHINA'S ISLAND CONSTRUCTION
Mattis said he would talk about the need for countries to uphold international law, an apparent reference to Beijing's construction activities on disputed islets and reefs in the South China Sea.
China's claims to most of 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.
Last week, a US Navy warship sailed within 12 nautical miles of an artificial island China has built on a disputed reef in the South China Sea, the first such challenge to Beijing in the strategic waterway since Trump took office.
The Trump administration has completed a broad review of US options aimed at curbing North Korea's nuclear and missile programme and leans more towards new sanctions and increased co-operation with Beijing.
Some Asian officials say worries about Trump's direction have been fueled by his unpredictable personal approach to policymaking and emphasis on his chemistry with Xi.
Since meeting Chinese President Xi Jinping in April, Trump has praised him for efforts to restrain North Korea.
"It is going to take time for the actions that China is taking to have affect in terms of North Korea," said David Helvey, a senior US defence official dealing with Asian and Pacific security affairs.
The United Nations Security Council will vote on Friday on a US and Chinese proposal to blacklist more North Korean individuals and entities after the country's repeated ballistic missile launches.
Mattis' trip also comes as South Korean President Moon Jae-in ordered an investigation this week into why his office had not been informed about the deployment of four more launchers for the US Terminal High Altitude Area Defence (THAAD) system.
Moon's top security aide left for Washington on Thursday as the new leader tries to reassure his country's main ally he will not scrap a deal to host a missile defence system that has angered China.
Helvey said the United States had consulted with South Korea throughout the process and had been transparent.