A Brazilian judge has ordered former President Jair Bolsonaro, who is currently under house arrest while awaiting the verdict in a coup-plotting trial, to be placed under round-the-clock observation.

Supreme Court Justice Alexandre de Moraes asked police to conduct "full-time surveillance" of the 70-year-old, declaring the far-right populist to be a "flight risk."

The tightened security comes as the final arguments in the case are expected early next month.

Bolsonaro faces up to 40 years in prison if convicted of plotting to cling to power after losing the 2022 presidential election to Luiz Inacio Lula da Silva.

He has denied the accusations and claimed he was facing political persecution.

Why is Bolsonaro under close surveillance?

On Tuesday, Moraes said police reinforcement is "appropriate and necessary" as the key phase of the trial approaches.

Explaining his decision, Moraes referred to a campaign being run by Bolsonaro's son, Eduardo, in the United States, which aims to lobby US authorities to intervene.

"The incessant activities of Eduardo Bolsonaro abroad show that there is a danger that Jair Bolsonaro could flee in order to evade the law," he said, also pointing to findings in a recent police report in which officers uncovered a draft of a 2024 letter from Bolsonaro requesting asylum in Argentina.

Tense US-Brazil relations 

This all comes amid heightened tensions between the US and Brazil.

Earlier Tuesday, Moraes and Justice Minister Ricardo Lewandowski had their US visas revoked by Washington over the Bolsonaro trial.

President Lula called the visa revocation an "irresponsible gesture" from the US. 

"These attitudes are unacceptable, not only against the minister but against all Supreme Court justices, against any Brazilian figure," he said at a Cabinet meeting.

US President Donald Trump has imposed crippling 50% tariffs on dozens of Brazilian imports, sanctioned Moraes and called the Bolsonaro trial a "witch hunt."

Edited by: John Silk