US officials said on Wednesday that they will sanction Brazilian Supreme Court judge Alexandre de Moraes, accusing him of authorising "arbitrary pre-trial detentions" and suppressing "freedom of expression".

Judge Moraes has been leading the investigation into allegations that Brazil's former right-wing President Jair Bolsonaro and his allies plotted a coup after he lost the 2022 election.

Bolsonaro has denied those allegations and has called Judge Moraes a "dictator".

Shortly after the sanctions were announced, US President Donald Trump signed an executive order that raised tariffs on Brazil to 50%.

Trump had threatened to impose the steep tariffs earlier this month in a letter he shared on social media to Brazil's current president, Luiz Inácio Lula da Silva.

In it, Trump accused Brazil of "attacks" on US tech companies and of conducting a "witch hunt" against Bolsonaro.

The executive order on tariffs excludes several of Brazil's major exports from the steep taxes, including orange juice, some aircraft parts and energy products.

The order also ties the tariffs directly to Brazil's "politically motivated persecution, intimidation, harassment, censorship and prosecution" of Bolsonaro.

Brazil has threatened to match any tariff imposed by the US.

The US is Brazil's second-largest trade partner after China, so the hike would hit the South American nation hard.

Brazil is the US's 15th largest trading partner, and among its main imports from the US are mineral fuels, aircraft and machinery.

For its part, the US imports gas and petroleum, iron, and coffee from Brazil.

When announcing the sanctions against Judge Moraes on Wednesday, US Secretary of the Treasury Scott Bessent accused Moraes of carrying out "an unlawful witch hunt against US and Brazilian citizens and companies."

Bessent added that the judge is "responsible for an oppressive campaign of censorship, arbitrary detentions that violate human rights, and politicized prosecutions – including against former President Jair Bolsonaro".

"Today's action makes clear that Treasury will continue to hold accountable those who threaten US interests and the freedoms of our citizens," he said.

The BBC has reached out to Judge Moraes for comment.

In addition to leading the investigation into Bolsonaro, Judge Moraes had previously ordered some social media accounts, including American ones, to be shut down for publishing disinformation.

The US president's company Trump Media, which operates his Truth Social platform, is among the US tech companies fighting Brazilian court rulings over orders suspending social media accounts.

The country had also briefly banned Elon Musk's X, formerly known as Twitter, after the platform refused to shut down accounts that were deemed by Brazil to be spreading misinformation about the 2022 Brazilian presidential election.

Last month, Brazil's Supreme Court ruled that social media companies can be held responsible for content posted on their platforms.

The latest sanctions mark a new escalation in an increasingly tense relationship between Brazil and the US under Trump's second term.

During Trump's first term, the US president and former Brazilian president Bolsonaro enjoyed a friendly relationship when their presidencies overlapped, and the two had met at the White House in 2019.

Both men subsequently lost presidential elections and both refused to publicly acknowledge defeat.

Bolsonaro, who governed Brazil between 2019 and 2022, is standing trial for allegedly attempting a coup with thousands of his supporters storming government buildings in the capital in January 2023 after Lula was victorious in the election.

Judge Moraes has imposed a raft of pre-trial restrictions on Bolsonaro, including a night-time and weekend curfew and 24-hour surveillance to prevent him from fleeing the country.

He has also been ordered to refrain from contacting foreign governments and their embassies in Brazil, and to wear an ankle tag.

Earlier in July, Trump compared Bolsonaro's prosecution to the legal cases he has similarly faced.

"This is nothing more, or less, than an attack on a Political Opponent - Something I know much about!" Trump had said. In response, Bolsonaro thanked the US president for his support.