SINGAPORE — U.S. Secretary of Defense Jim Mattis has arrived in Asia on the eve of a major regional security summit as Asia-Pacific allies call for the United States to outline its commitment to the region in the face of a myriad security challenges.

Mattis will speak June 3 at the morning plenary sessions at this year's iteration of the annual IISS Shangri-La Dialogue in Singapore, which will take place June 2-4.

The plenary sessions at the event will examine the role of the United States in the Asia-Pacific, geopolitical change and defense policy, crisis management in the region, and other topics. There will also be special sessions on nuclear dangers and emerging technology, with regional and global senior defense officials poised to speak at the event.

The dialogue is organized by the International Institute for Strategic Studies, or IISS, and is currently the largest gathering of defense professionals in the Asia-Pacific region. This year's event will see more than 500 delegates — representing 32 nations from across the Asia-Pacific and beyond — converge in Singapore to examine the region's most enduring security challenges.

Tim Huxley, executive director of IISS-Asia in Singapore, said he has been told Mattis will deliver a "concise, punchy" speech. Earlier reports indicated the defense secretary will discuss North Korea, pressing for greater regional cooperation to contain the isolated regime's nuclear and missile program.

If this is the case, it will be in contrast to previous years, where the U.S. has tried to focus the spotlight on China's expansion and assertive behavior in the strategic South China Sea.

However, regional allies and partners will be keen for Mattis to outline the Trump administration's policy in the Asia-Pacific. Huxley and Benjamin Schreer, who heads the Department of Security Studies and Criminology at Australia's Macquarie University, warned in a recent article for the Australian Strategic Policy Institute that failing to do so will fuel "the perception — particularly in Southeast Asia — that the United States is effectively ceding its regional leadership to China," and this perception "will only become more pervasive and more influential with regard to Asian countries' policy choices."

Australian Prime Minister Malcolm Turnbull struck a similar tone in his keynote address at the event, where he expects the Trump administration will "recognize, as its predecessors have, that the United States' own interests in the Indo-Pacific demand more U.S. engagement, not less," noting that the "peace and stability of our region has been enabled by consistent U.S. global leadership". 

He also called the United States' decisions to withdraw from the Trans-Pacific Partnership and the Paris Agreement on climate change "disappointing." But he also urged the audience "not to rush to interpret an intent to engage on different terms as one not to engage at all."

Another issue that will likely come up at the summit will be the Philippines' ongoing battle with Islamic State group-linked Maute militants in the southern part of the country, where the Army is struggling to take back the central Mindanao town of Marawi, which was overrun following a failed attempt to arrest the group's leader in the town in late May.

Mike Yeo is the Asia correspondent for Defense News.

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