In a letter addressed to Brazilian President Luiz Inacio Lula da Silva, Trump criticized the treatment of his right-wing ally Jair Bolsonaro as an "international disgrace."

Bolsonaro is facing trial over accusations he plotted a coup after his narrow 2022 election loss to Lula.

In response to Trump's tariff letter, Lula warned of possible reciprocation, writing on social media that "any unilateral tariff increases will be addressed in light of the Brazilian Law of Economic Reciprocity."

Brazil said earlier on Wednesday it had summoned the US charge d'affaires over Trump's previous criticism of the Bolsonaro trial.

The 50-percent US tariff on Brazilian goods will take effect August 1, Trump said in his letter, mirroring a deadline that dozens of other economies face.

On that same date, a 50-percent tariff on US imports of copper -- a key metal used in green energy and other technologies -- will take effect, Trump announced Wednesday evening on social media.

He said the move followed a "robust NATIONAL SECURITY ASSESSMENT," likely alluding to a Department of Commerce investigation into copper launched this year.

"Copper is the second most used material by the Department of Defense!" Trump said.

- Escalation threats -

Trump's message to Lula was the latest in more than 20 such letters the US president has released since Monday, after repeatedly threatening to simply decide a rate for countries as negotiations continue over his elevated "reciprocal" tariffs.

Brazil had not been among those threatened previously with duties above a 10-percent baseline, and the United States runs a goods trade surplus with Brazil.

China said in response that "arbitrary" tariffs such as the 50-percent levy on copper "serve no party's interests".

"We have always opposed the overstretching of the concept of national security," foreign ministry spokeswoman Mao Ning told a regular news conference.

On Wednesday, Trump also addressed letters to leaders of the Philippines, Sri Lanka, Brunei, Algeria, Libya, Iraq and Moldova, spelling out duties ranging from 20 percent to 30 percent that would also take effect on August 1.

Similar to a first batch of documents published Monday, the levels were not too far from those originally threatened in April, although some partners received notably lower rates this time.

While Trump in April imposed a 10-percent levy on almost all trading partners, he unveiled -- and then withheld -- higher rates for dozens of economies.

The deadline for those steeper levels to take effect was meant to be Wednesday, before Trump postponed it further to August 1.

Countries that faced the threats of elevated duties began receiving letters spelling out US tariff rates on their products.

In the messages, Trump justified his tariffs as a response to trade ties that he says are "far from Reciprocal."

The letters urged countries to manufacture products in the United States to avoid duties, while threatening further escalation if leaders retaliated.

Other countries that have received Trump's letters include key US allies Japan and South Korea, as well as Indonesia, Bangladesh and Thailand.

- EU deal in 'coming days'? -

Analysts have noted that Asian countries have been a key target so far.

But all eyes are on the state of negotiations with major partners who have yet to receive such letters, including the European Union.

European stock markets rose at the start of trading on Thursday, with London hitting a fresh record high on optimism that governments will strike deals to avoid the worst of US tariffs.

The Trump administration is under pressure to unveil more trade pacts. So far, Washington has only reached agreements with Britain and Vietnam, alongside a deal to temporarily lower tit-for-tat levies with China.

Trump said on Tuesday his government was "probably two days off" from sending the EU a letter with an updated tariff rate.

An EU spokesperson said Wednesday the bloc wants to strike a deal with the United States "in the coming days," and has shown readiness to reach an agreement in principle.

Apart from tariffs targeting goods from different countries, Trump has rolled out sector-specific duties on steel, aluminum and autos since returning to the White House in January.