The highest court in Belarus has convicted an aspiring rival to the nation’s authoritarian president on corruption charges and sentenced him to 14 years in prison.

Viktor Babariko, the head of a commercial bank owned by Russian natural gas company Gazprom, had hoped to challenge Alexander Lukashenko last year, but was arrested before the August presidential election and prohibited from registering as a candidate.

At the time, he was widely perceived as Mr Lukashenko’s main rival, and his arrest drew thousands of protesters on to the streets.

On Tuesday, Belarus’s Supreme Court convicted Mr Babariko on charges of taking a bribe and money laundering and handed him a 14-year prison sentence and a fine of about £41,000.

Mr Babariko, who served as the chief executive of Belgazprombank, has remained jailed since his arrest. He dismissed the corruption charges as politically motivated.

“I can’t plead guilty to the crimes I didn’t commit,” he told the court before it issued the verdict. “I can tell you from that cage that I don’t feel ashamed for my life before the people I knew.”

The US Embassy denounced the verdict as a “cruel sham”, saying on Twitter it showed that Mr Lukashenko’s “regime will stop at nothing to keep power”.

The president’s re-election to a sixth term was widely seen as rigged and triggered months of protests, the largest of which drew up to 200,000 people.

Authorities responded to the demonstrations with a massive crackdown that saw more than 35,000 people arrested, thousands beaten by police and opposition leaders jailed or forced to leave the country.

The EU and the US responded to the crackdown by slapping Belarus with sanctions, and imposed tougher restrictions after Belarus diverted a passenger jet on May 23 to arrest an opposition journalist.

Speaking in Brussels on Tuesday, European Commission spokesman Peter Stano said Mr Babariko’s “sentence is one of at least 125 unfair and arbitrary recent verdicts by Belarusian courts in politically motivated trials, often held behind closed doors and without due process of law”.

Mr Stano added that “serious human rights violations come at a price”, and said the EU “stands ready to consider further measures” beyond the sanctions already imposed on Belarus officials and businesses.

He said the EU demands Mr Babariko be immediately released, along with “all political prisoners, detained journalists and people who are behind bars for exercising their fundamental rights”. “The regime must halt repression and injustice and hold perpetrators to account,” he added.

Sviatlana Tsikhanouskaya, who ended up as the main opposition candidate, denounced what she described as a “mad sentence to the person who decided to enter politics and became one of the leaders who woke the country up from a long sleep”.

“The regime is doing all that in order to kill any thoughts even distantly resembling faith and hope,” said Ms Tsikhanouskaya, who was forced to leave Belarus under official pressure after the election.

“But the hope in our hearts is something that is the most precious for Viktor and thousands of other innocent people in prisons.”