Updated June 2, 2023 at 12:43 PM ET

SINGAPORE – Tense U.S.-relations and an arms build-up in the Pacific region will be on show this weekend as defense chiefs, including from the U.S. and China, gather at the Shangri-La Dialogue, an international defense summit, in Singapore.

The Dialogue, which started Friday, has been overshadowed by China's refusal to let its defense minister meet formally with U.S. Secretary of Defense Lloyd Austin at the forum. But both countries are still leading large delegations to the summit, which gathers diplomats, academics, defense contractors, journalists, and analysts from around the Pacific region.

Here's what else to look out for at the Shangri-La Dialogue this weekend.

The U.S. and China are headlining the event

Although Chinese defense minister Li Shangfu and Austin weren't expected to speak to each other, the two defense chiefs did briefly exchange words and shook hands before being seated at Friday's opening dinner — "but did not have a substantive exchange," Pentagon spokesperson Pat Ryder said in statement.

Li was sanctioned by the U.S. in 2018, when he was heading the Chinese military's equipment development division, for purchasing weapons from a sanctioned Russian institution. China has indicated it will not agree to a meeting unless those sanctions are first lifted.

China's refusal dampened hopes that recent bilateral meetings could mend some of the frictions between the two superpowers. Last month, U.S. national security adviser Jake Sullivan was able to meet his counterpart, China's top diplomat, Wang Yi, in Vienna. That meeting was quickly followed by talks between the two country's commerce chiefs.

This week in Tokyo, Austin told his Japanese counterpart, Defense Minister Hamada Yasukazu, that it was "unfortunate" China declined the American invitation for their two chiefs to meet. He pointed to an incident late last month, in which a Chinese fighter jet allegedly buzzed an American aircraft flying over the South China Sea by cutting in front of it at close range, as reason for talks.

"We would hope that they would alter their actions. But since they haven't yet, I'm concerned about, at some point, having an incident that could very, very quickly spiral out of control," Austin said.

Meanwhile, representatives from the U.S. and Taiwan signed a trade agreement on the eve of the security summit and over protests from China, which claims the island as part of Chinese territory. The pact was signed by workers of unofficial entities that maintain relations between the U.S. and the island democracy.

A competition for regional alliances

Both the U.S. and China are hustling to strengthen partnerships with Asia-Pacific countries as they build up their military capacity in the region.

"In addition, based on the severe and complex security environment, we confirmed the importance to deepen cooperation not only between Japan and the United States, but also with Republic of Korea, Australia and ASEAN countries," Austin said during his visit this week to Japan. Austin, the U.S. defense chief, is currently on his seventh tour of the Asia Pacific region.

So far, most Southeast Asian countries have tried not to tilt too much in favor toward China or the U.S., and have participated in the proliferating number of joint military drills with both countries. But China has watched with trepidation as the U.S. has forged stronger defense ties with two of Southeast Asia's most populous countries, Indonesia and the Philippines.

Indonesia, the U.S., and 12 other nations held massive military exercises together last fall. Earlier this year, the U.S. also stepped up its military presence in the Philippines by increasing its training exercises there and expanding the number of Philippines' military bases utilized by the American military from five to nine.

The deepening U.S.-China military competition has drawn in surrounding countries, whose concerns will be front and center at the Shangri-La Dialogue. Australian Prime Minister Anthony Albanese delivers a keynote address at the opening dinner on Friday. Japan, a key U.S. ally which has been deeply concerned over China's increasing hostility toward the nearby island of Taiwan, has sent a large delegation.

The dialogue comes at an important moment in Southeast Asian politics

For smaller Southeast Asian countries, the dialogue is chance to hash out foreign policy and engineer informal meetings between officials on the sidelines of closed-door talks, and more than a quarter of the summit's delegates hail from the region.

In Thailand, a surprise win by the opposition party during recent national elections could lead to an opening on a more aggressive foreign policy approach to supporting opposition forces in Myanmar, where the military seized power in a coup in 2021.

Southeast Asia is also maneuvering around how to position themselves around the great power rivalry between the U.S. and China. The South China Sea, where China has staked out contested territorial claims at odds with overlapping claims from Vietnam, the Philippines, and Malaysia, to name just a few, remains a hot button issue.

Taiwan and its dominance in semiconductor manufacturing – a critical tech sector at the heart of the U.S.-China rivalry – is also an issue of concern for Southeast Asia. Some U.S. firms and Taiwanese chip juggernaut TSMC have been looking to shift operations to the region, out of China.

The war in Ukraine, despite being a hemisphere away, will also be on the agenda. Most Southeast Asian countries have chosen to remain silent on Russia's invasion. Ukraine has sent its deputy defense chief, Volodymyr Havrylov, to Singapore to attend the summit, where he will speak on a panel with Andi Widjajanto, a politician from Indonesia, which has kept up friendly ties with Moscow.

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