Pentagon chief Pete Hegseth is the headline speaker at Asia's premier defence summit, which began on Friday with top Chinese officials notably absent despite weighty questions over Taiwan and the war in Iran.
Beijing's defence minister is skipping the three-day Shangri-La Dialogue in Singapore for the second year running, which analysts viewed as a sign of China's rising power.
The forum brings together top officials from around 45 nations and has historically provided a setting for debate as well as both quiet and high-profile diplomacy.
But the absence of China's Dong Jun means no meeting with Hegseth, even as Beijing tests American commitment to Taiwan and Washington seeks an end to the Middle East war.
Vietnamese leader To Lam called on countries to make such talks "truly effective instruments of risk reduction", adding in a keynote address on Friday evening that the Shangri-La Dialogue should not become a platform for merely "restating positions".
He urged "responsible commitment" from influential nations "both within and beyond the region", without mentioning the United States or China by name.
"Competition must be bounded by law, guided by transparency and exercised with restraint," Lam said.
He also said Vietnam's position on the South China Sea, where it has a territorial dispute with Beijing, remained "clear, consistent and principled".
Recently elected president and Communist Party leader -- a dual role evoking China's Xi Jinping -- Lam is Vietnam's most powerful leader in decades.
Hegseth's second trip to the forum comes after US President Donald Trump's visit to China this month.
Trump said the countries struck "fantastic" trade deals, although details have been vague, and he has suggested Washington could use arms sales as a bargaining chip with Beijing.
Hegseth's speech on Saturday is expected to be "quite strong against China, but mainly for internal (US) consumption", said Oh Ei Sun, senior fellow at the Singapore Institute of International Affairs.
China sent Dong to the dialogue as recently as 2024, when he and then Pentagon chief Lloyd Austin met for their first substantive face-to-face talks in 18 months.
But Dong was absent last year, and China said on Thursday it would send experts and scholars from its army's academic institutions this time.
Major General Meng Xiangqing of the National Defense University is leading a delegation that also includes scholars from the Academy of Military Sciences and the Navy.
"China has truly arrived as a major power in the region, so it does not really need to send its defence minister to brave a fusillade of questions," said William Choong, principal fellow at the ISEAS-Yusof Ishak Institute think tank.
Two other former defence ministers, Wei Fenghe and Li Shangfu, previously spoke at Shangri-La. Both have since been handed suspended death sentences on graft charges.
"It's kind of a poisoned chalice for any Chinese defence minister to speak out publicly," said Jennifer Parker, adjunct professor at the University of Western Australia's Defence and Security Institute.
But Beijing also risks not having a senior leader present if two of the most pertinent global security issues -- Taiwan and the opening of the Strait of Hormuz -- do come up.
The defence ministers of the United States, Britain and Australia -- the members of the AUKUS security alliance -- are also due to convene.
AUKUS's stated goal is to ensure a free and open Asia-Pacific region, although it is widely seen as a bulwark against a rising China and is strongly opposed by Beijing.
Australian Defence Minister Richard Marles said on Friday that Canberra was seeking "the maintenance of the global rules-based order" in the region.
"We've seen China engage in a very significant military buildup... and it has not happened with the kind of strategic reassurance which (we) would expect," he told journalists.
Australian media outlets have reported, citing unidentified sources, that the AUKUS nations are expected to announce a major project, perhaps involving uncrewed underwater vehicles.
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