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 per cent 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 per cent tariff, Laos and Myanmar 40 per cent, Cambodia and US ally Thailand 36 per cent, and Indonesia 32 per cent.
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 a 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 prioritise 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 theatre 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 finalising 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 per cent tariff on any that align themselves with "anti-American" policies.
The BRICS countries include Indonesia, as well as China and India.
Last week, Trump announced he had reached a trade agreement with important Southeast Asian partner and ASEAN member Vietnam and could reach one with India. But he cast doubt on a possible deal with Japan, which is not only Washington's main Asian ally, but a major investor in the US.
Rubio has yet to visit Japan, or South Korea, the other main US ally in Northeast Asia, since taking office in January, even though Washington sees the Indo-Pacific as its main strategic priority given the perceived threat from China.
South Korea's presidential security adviser Wi Sung-lac headed to Washington on Sunday for trade and defence talks, with Seoul seeking to head off US tariffs.
He aims to meet with Rubio and discuss a possible summit between Trump and President Lee Jae Myung, who took office in June.
