The Trump administration is promising an unspecified “response” to what it is calling the unjust conviction and sentencing of the defeated president of Brazil, Jair Bolsnaro, who faces more than 27 years in prison after this week’s swift trial on charges of attempting a coup to remain in power.

Posting on X late Thursday, the secretary of state, Marco Rubio, took particular aim at one of the five judges who presided over the trial, Alexandre de Moraes.

“The political persecutions by sanctioned human rights abuser Alexandre de Moraes continue, as he and others on Brazil’s supreme court have unjustly ruled to imprison former President Jair Bolsonaro,” Mr. Rubio wrote. “The United States will respond accordingly to this witch hunt.”

Brazil’s foreign ministry rejected Mr. Rubio’s comment as a threat that “attacks Brazilian authority and ignores the facts and the compelling evidence in the records,” Reuters reported. It quoted the ministry saying Brazilian democracy would not be intimidated by the United States.

While Mr. Rubio remained vague about the nature of any action, the White House spokeswoman, Karoline Leavitt, suggested the possibility of economic or military retaliation when asked how America might respond to the Bolsonaro trial earlier in the week.

“Freedom of speech is arguably the most important issue of our time. It is enshrined in our Constitution and the president believes in it strongly. … We have taken significant action with regards to Brazil in the form of both sanctions, and also leveraging the use of tariffs,” Ms. Leavitt said at a briefing on Tuesday.

“This is a priority for the administration, and the president is unafraid to use the economic might, the military might of the United States of America, to protect free speech around the world.”

President Trump was more restrained in his own reaction to the conviction Thursday, saying, “Well, I watched that trial. I know him pretty well — foreign leader. I thought he was a good president of Brazil, and it’s very surprising that could happen very much like they tried to do with me, but they didn’t get away with it at all.”

Even before the trial, the Trump administration had acted to punish Brazil and some of the individuals involved for the prosecution of Bolsonaro, a right-wing populist who served as president between 2019 and his defeat in elections in October 2022.

Mr. Trump announced in July a 50 percent tariff on imports from Brazil, which he said was due “in part to Brazil’s insidious attacks on Free Elections, and the fundamental Free Speech Rights of Americans.” That same month, the state department announced sanctions on Justice De Moraes, whom it accused of “suppressing freedom of expression and politicizing prosecutions.”

Brazil’s current president, Luiz Inacio Lula da Silva, responded that “the defense of democracy in Brazil is a matter for Brazilians. We are a sovereign nation. We won’t accept interference or instruction from anyone. We have solid and independent institutions. No one is above the law. Especially those who attack freedom and the rule of law.”

Four of the five judges hearing the case found Bolsonaro guilty on all five charges against him, which included attempting a coup to remain in power; involvement in an armed criminal organization; attempting to violently abort Brazil’s democratic rule of law; committing violent acts against state institutions, and damaging protected public property.

Several alleged co-conspirators, including Bolsonaro’s former defense minister and 2022 running mate, General Braga Netto, received sentences ranging up to 26 years.

Bolsonaro had refused to concede defeat in a runoff election against Mr. Lula da Silva, creating a period of instability not unlike that following President Trump’s election defeat two years earlier. At one point a pro-Bolsonaro mob stormed the nation’s legislature, supreme court, and presidential palace.

Evidence presented at the trial accused Bolsonaro of plotting with political and military leaders to suspend the election results and seeking the assassination of Mr. Lula da Silva, Vice President Geraldo Alckmin, and Justice Moraes.

Bolsonaro remains under house arrest, where he has been since August pending a possible appeal to the full supreme court. The trial court must publish its formal ruling within 60 days, after which Bolsonaro’s lawyers have five days to request a clarification of the ruling.

Under Brazilian law, an appeal is normally not possible if more than three judges on a five-judge panel vote to convict, but analysts say there is a chance that appeal would be granted because of the unusual circumstances of the case.