Rubio met in Washington with his counterparts from the so-called Quad a day after the inauguration of President Donald Trump, who has vowed to push back against a rising China.

But the gathering also marks a contrast with Trump's frequent dismissal of US allies and partners, with the returning US president on Tuesday threatening tariffs against the European Union.

Rubio and his counterparts in a joint statement promised to work toward a "free and open Indo-Pacific," deploying a codeword against Chinese aggression that has been utilized by US administrations from both major political parties.

The four said they support a region "where the rule of law, democratic values, sovereignty and territorial integrity are upheld and defended."

"We also strongly oppose any unilateral actions that seek to change the status quo by force or coercion," the statement said.

The ministers also confirmed they would work to hold a Quad summit previously scheduled for this year in India, which would mean an early trip by Trump to the growing US partner often viewed in Washington as a bulwark against China.

Trump in his first term formed a strong bond with Hindu nationalist Prime Minister Narendra Modi, who regaled him with a massive rally together at a cricket stadium.

China has had rising friction with the Philippines, a US ally, over its assertive claims in territorial disputes.

Rubio in his confirmation hearing also vowed to deter China against an invasion of Taiwan, the self-governing democracy it claims as its own.

Trump during the campaign rattled Taiwan by saying it needed to pay the United States protection money, and Trump's nominee for defense secretary, Pete Hegseth, made headlines at his confirmation hearing by not being able to name a member of ASEAN, the Association of Southeast Asian Nations.

The Quad was envisioned by late Japanese prime minister Shinzo Abe and expanded into a leaders' summit by former president Joe Biden.

China has repeatedly lashed out at the Quad, saying it is a US plot to encircle the rising Asian power.

- When interests align -

Rubio, a three-term senator who a day earlier was unanimously confirmed by his peers, arrived at the State Department with a promise to defend US diplomats -- often maligned by his Republican Party -- while also pursuing Trump's belief in "America First."

"I expect every nation on earth to advance their national interests. And in those instances -- and I hope there will be many -- in which our national interests and theirs align, we look forward to working with them," Rubio said.

"We recognize that there will be those times unfortunately as humans interact with one another because of our nature that there will be conflict," Rubio said.

"We will seek to prevent them and avoid them, but never at the expense of our national security," he said.

With Trump's return, a slew of senior career diplomats quit their posts at the State Department as the new administration pushes to bring in political appointees it sees as loyal.

Addressing employees with his wife and four children by his side, Rubio said: "There will be changes."

"But the changes are not meant to be destructive, they're not meant to be punitive," he said.

"But we need to move faster than we ever have because the world is changing faster than we ever have."