Hegseth's headline speech at Singapore's Shangri-La Dialogue, which brings together top defence officials and experts from about 45 countries, contrasted with his strongly confrontational remarks on China at last year's gathering.

It came as Donald Trump struggles to resolve the Middle East war -- which has caused oil prices to soar, hurting major Asian economies -- and after the US president met his Chinese counterpart Xi Jinping against the perennial background of tensions over Taiwan.

"When we look across the region today, there is rightful alarm regarding China's historic military build-up and the expansion of its military activities in the region and beyond," Hegseth said.

Washington does not seek "needless confrontation" but rather "a genuinely stable equilibrium (in Asia) that works for Americans as well as our allies", he said.

That means "a favourable but durable balance of power in which no state, including China, can impose its hegemony and hold the security or prosperity of our nation and our allies in question", according to Hegseth.

Unlike Beijing, which has sent a panel of military experts and scholars instead of Defence Minister Dong Jun for the second year running, Hegseth is leading a bumper US delegation to the event that provides chances for both open debate and closed-door diplomacy.

The Pentagon chief said the United States sought "respectful" and "good-faith" engagement with Beijing, adding: "I wish my counterpart was here at this conference, but I look forward to other options when we can cross paths."

Major General Meng Xiangqing, the head of the Chinese delegation, said following the speech that "stable US-China relations are not only good for both peoples, but also good for regional stability and global peace".

- Vibe shift -

Trump visited China this month, talking up "fantastic" trade deals but giving few details and later suggesting Washington could use its arms sales to self-ruled Taiwan as a bargaining chip with Beijing.

There had been "no change" in Washington's stance towards Taiwan, but "any decision about future Taiwan arms sales... will rest with" Trump, Hegseth said.

His remarks about the regional state of affairs contrasted sharply with last year's event, when Hegseth painted China as a potentially "imminent" threat to security and outlined a swaggering vision of muscular American deterrence.

Chinese delegate Da Wei, director of the Center for International Security and Strategy at Beijing's Tsinghua University, told AFP this year's address was "much more moderate".

However, he said Hegseth's depiction of a hegemonic China was "ironic... given what the US is doing in Iran and has done in Venezuela."

US delegate Tammy Duckworth, a Democratic senator and Trump critic, said Hegseth's remarks were overly conciliatory towards China.

"I worry that this administration is being distracted into wars that they've started in other parts of the world at the expense of our commitment here in the Indo-Pacific," she told reporters.

Instead of Dong, China has sent experts and scholars from its army's academic institutions, led by Meng of the National Defense University.

Analysts have said Dong's no-show reflects Beijing's confidence as an established power with little inclination to answer publicly for its assertive moves in the region.

- Iran threat -

Some argue, however, that China is also running the risk of having no senior policymaker present if two major security issues come up: reopening the Strait of Hormuz, and Beijing's claim to Taiwan.

Hegseth praised nations including South Korea, Japan, Australia and the Philippines for boosting their defence spending, while threatening consequences for nations that "free-ride".

"Those days are over. Allies who refuse to step up and carry their own weight for our collective defence will face a clear shift in how we do business."

Hegseth's remarks came as a peace deal between the United States and Iran to end their war remained elusive.

A White House official told AFP on Friday that Trump, who is weighing a final decision on a potential accord, would only commit if Iran met all his conditions.

But Iran has said "no final agreement" is in place, and its state media has rebutted parts of Trump's characterisation of the deal.

Hegseth said Washington was "more than capable" of restarting the war if it wanted.

Separately, Hegseth and his British and Australian counterparts announced that they would team up under their AUKUS security alliance to develop payloads for undersea drones.

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