The State Department billed the July 8-12 trip as a move to reaffirm Washington's commitment to the Indo-Pacific. Hours later, Trump said he would impose 25 percent tariffs from August 1 on imports from Japan and South Korea, the key US regional allies and vital partners in countering China's growing might.

Trump also announced plans for tariffs on Malaysia and five other countries in the 10-member Association of Southeast Asian Nations, whose ministers Rubio will join for meetings in the Malaysian capital Kuala Lumpur. 

Malaysia faces a 25 percent tariff, Laos and Myanmar 40 percent, Cambodia and US ally Thailand 36 percent, and Indonesia 32 percent.

Rubio will seek to firm up US relationships with partners and allies unnerved by Trump's global tariff strategy. Trump's announcements seemed certain to make that task harder.

The trip has been seen as part of renewed US focus on the Indo-Pacific and an effort to look beyond conflicts in the Middle East and Europe that have consumed much of the Trump administration's attention.

"Top topics that he's going to want to hit, obviously, are to reaffirm our commitment to East Asia, to ASEAN, to the Indo-Pacific, and not just ... for its own sake," a senior State Department official told reporters.

"I think a key message that the secretary likes to deliver is that we're committed, and we prioritize it because it is in America's interests, right? It promotes American prosperity and it promotes American security."

The official said Rubio would be prepared to discuss trade, including reiterating that the need to rebalance US trade relationships is significant and echoing messages from the White House and the US Trade Representative.

ASEAN countries have been nervous about Trump's tariffs and questioned the willingness of his "America First" administration to fully engage diplomatically and economically with the region.

"There is a hunger to be reassured that the US actually views the Indo-Pacific as the primary theater of US interests, key to US national security," said Greg Poling, director of the Southeast Asia Program at Washington's Center for Strategic and International Studies.

On Sunday, Trump said the US was close to finalizing several trade pacts and would notify other countries by July 9 of higher tariff rates.

He also sent a message to BRICS group of developing nations as its leaders met in Brazil, threatening an additional 10 percent tariff on any that align themselves with "anti-American" policies.

The BRICS countries include Indonesia, as well as China and India.

ASEAN nations will express "concern" over "counterproductive" US tariffs, according to a draft statement shared with AFP on Tuesday, after Donald Trump threatened more than a dozen countries with higher levies. 

"We expressed concern over rising global trade tensions and growing uncertainties in the international economic landscape, particularly the unilateral actions relating to tariffs," ASEAN foreign ministers said, according to a draft Joint Communique.

Without directly naming the United States, the ministers said tariffs were "counterproductive and risk exacerbating global economic fragmentation and pose complex challenges to ASEAN's economic stability and growth".