US Secretary of State Marco Rubio took part in the meeting in New Delhi, 10 days after President Donald Trump paid a friendly state visit to China and spoke glowingly of the two powers working together as a "G2" -- a concept that the US partners, which view Beijing's rise warily, fear could shut them out.

Meeting his counterparts in the Indian capital, Rubio said the Quad comprised countries "who share strong values -- strong, vibrant democracies -- who also are committed to many of the same concepts with regards to economic development and have many aligned interests".

The Quad said in a joint statement members would together mobilise $20 billion in government and private money to strengthen critical mineral supply chains, including by identifying projects in the four countries. It was unclear if that would be entirely new funding.

Critical minerals mark a rare area in which the Trump administration has turned to the more traditional diplomacy of building networks with allies, alarmed at the dominance of China in resources central to the high-end technology sector.

Rubio said the four powers would also work together on two maritime initiatives -- one that combines their surveillance capabilities, and another that will provide enhanced real-time information to commercial traffic at sea.

In a first, Australian Foreign Minister Penny Wong said the Quad was cooperating on assisting port development in Fiji -- a key island nation in the South Pacific, where China has made a concerted push for greater influence.

"We recognise our obligation -- our responsibility -- to provide real choices, particularly as strategic circumstances in our region are deteriorating," Wong said.

Reacting to the meeting, Chinese foreign ministry spokeswoman Mao Ning said that cooperation "should not be directed against any third party".

"We also do not support exclusive cliques or bloc confrontations," she told reporters.

Trump has been dismissive of major allies, repeatedly saying they unfairly burden the United States financially.

While Rubio held two Quad meetings last year, including one hours after taking office, Trump declined to commit to a four-way leaders' summit.

It marked a strong contrast to his predecessor Joe Biden, who put a priority on alliances and vowed that Quad summits were "here to stay".

Rubio said the Trump administration wanted the Quad to focus more on deliverables than meetings, and said cooperation was progressing "pretty aggressively".

- Disagreement on Iran -

Freedom of navigation has long been Washington's codeword for opposing China's assertiveness at sea, a particular concern for Japan.

But the United States has recently pointed to the principle as it tries to rally allies to counter Iran, which has exerted control over the strategic Strait of Hormuz in response to the US-Israeli war launched on February 28 and which sent global oil prices spiralling.

No US ally other than Israel has robustly supported the decision to attack Iran, enraging Trump, who has questioned the reliability of US partners he had not consulted beforehand.

India's Foreign Minister Subrahmanyam Jaishankar said the focus of the talks would be "the Indo-Pacific, which is the specific limit of the Quad".

Besides Iran, India has differed with the other Quad nations on Russia's invasion of Ukraine by refusing to sever its long-standing relationship with Moscow.

Australia's Wong said there was much to focus on in Asia, due to its "deteriorating strategic environment and acute economic stress".

Australian Prime Minister Anthony Albanese is one of the few world leaders who has voiced some understanding for the Iran war, citing concerns about Tehran's disputed nuclear programme, but he has not assisted the war effort and Trump said he was "not happy with Australia".

Japan and India have historically both maintained cordial relations with Iran, although they grudgingly complied with US sanctions on Iranian oil.