WASHINGTON — President Donald Trump on Monday set a 25% tax on goods imported from Japan and South Korea, as well as new tariff rates on a dozen other nations that would go into effect on Aug. 1.

Trump provided notice by posting letters on Truth Social that were addressed to the leaders of the various countries. The letters warned them to not retaliate by increasing their own import taxes, or else the Trump administration would further increase tariffs.

“If for any reason you decide to raise your Tariffs, then, whatever the number you choose to raise them by, will be added onto the 25% that we charge,” Trump wrote in the letters to Japanese Prime Minister Shigeru Ishiba and South Korean President Lee Jae-myung.

The letters were not the final word from Trump on tariffs, so much as another episode in a global economic drama in which he has placed himself at the center. His moves have raised fears that economic growth would slow to a trickle, if not make the U.S. and other nations more vulnerable to a recession. But Trump is confident that tariffs are necessary to bring back domestic manufacturing and fund the tax cuts he signed into law last Friday.

He mixed his sense of aggression with a willingness to still negotiate, signaling the likelihood that the drama and uncertainty would continue and that few things are ever final with Trump.

Imports from Myanmar and Laos would be taxed at 40%, Cambodia and Thailand at 36%, Serbia and Bangladesh at 35%, Indonesia at 32%, South Africa and Bosnia and Herzegovina at 30% and Kazakhstan, Malaysia and Tunisia at 25%.

Trump placed the word “only” before revealing the rate in his letters to the foreign leaders, implying that he was being generous with his tariffs. But the letters generally followed a standard format, so much so that the one to Bosnia and Herzegovina initially addressed its woman leader, Željka Cvijanović, as “Mr. President.” Trump later posted a corrected letter.

White House press secretary Karoline Leavitt said that Trump was by setting the rates himself creating “tailor-made trade plans for each and every country on this planet and that’s what this administration continues to be focused on.”

Following a now well-worn pattern, Trump plans to continue sharing the letters sent to his counterparts on social media and then mail them the documents, a stark departure from the more formal practices of all his predecessors when negotiating trade agreements.

The letters are not agreed-to settlements but Trump’s own choice on rates, a sign that the closed-door talks with foreign delegations failed to produce satisfactory results for either side.

Wendy Cutler, vice president of the Asia Society Policy Institute who formerly worked in the office of the U.S. Trade Representative, said the tariff hikes on Japan and South Korea were “unfortunate.”

“Both have been close partners on economic security matters and have a lot to offer the United States on priority matters like shipbuilding, semiconductors, critical minerals and energy cooperation,” Cutler said.

Trump still has outstanding differences on trade with the European Union and India, among other trading partners. Tougher talks with China are on a longer time horizon in which imports from that nation are being taxed at 55%.

The office of South African President Cyril Ramaphosa said in a statement that the tariff rates announced by Trump mischaracterized the trade relationship with the U.S., but it would “continue with its diplomatic efforts towards a more balanced and mutually beneficial trade relationship with the United States” after having proposed a trade framework on May 20.

The S&P 500 stock index was down 0.8% in Monday trading, while the interest charged on 10-year U.S. Treasury notes had increased to nearly 4.39%, a figure that could translate into elevated rates for mortgages and auto loans.

Trump has declared an economic emergency to unilaterally impose the taxes, suggesting they are remedies for past trade deficits even though many U.S. consumers have come to value autos, electronics and other goods from Japan and South Korea. The constitution grants Congress the power to levy tariffs under normal circumstances, though tariffs can also result from executive branch investigations regarding national security risks.