One of Belarus's leading opposition figures was sentenced to 14 years in prison on Tuesday, the latest move in a months-long crackdown on critics of strongman leader Alexander Lukashenko.

Former banker Viktor Babaryko -- considered one of Lukashenko's strongest opponents -- was handed the sentence by the Supreme Court in Minsk.

His Twitter account, which is run by supporters, said he would serve the 14 years "in a maximum security colony".

The 57-year-old was arrested in June last year on fraud charges ahead of a disputed presidential election that sparked several months of protests.

He had planned to run in the election and was considered the strongest challenger to Lukashenko's almost three decade rule.

Babaryko was accused of receiving bribes and of money laundering when he was head of Belgazprombank, the Belarusian branch of a bank belonging to Russian energy giant Gazprom.

He was also ordered to pay 46 million Belarusian rubles ($18 million, 15 million euros) in damages, according to local independent rights group Viasna.

Exiled opposition leader Svetlana Tikhanovskaya called the verdict "insane" and said it was aimed at silencing Babaryko.

"14 years for faith in an idea," Tikhanovskaya wrote on the Telegram messaging app. She herself fled abroad after having claimed victory against Lukashenko in the election.

"The regime is doing everything to kill ideas in us that are even remotely similar to hope."

The EU demanded the immediate release of Babaryko and the US embassy in Minsk denounced the sentence as a "sham" that showed "the Lukashenko regime will stop at nothing to keep power".

Western diplomats attended the hearing, according to Viasna, which said two people were detained outside the court after "dozens" of Babaryko supporters arrived at the building but were refused entry to the courtroom.

Amnesty International said Babaryko had "been targeted because he dared to challenge Alexander Lukashenko and is now paying the price for his courage with his liberty".

Before his arrest, Viktor Babaryko was considered one of the strongest opponents to strongman Alexander Lukashenko in last year's presidential vote
Before his arrest, Viktor Babaryko was considered one of the strongest opponents to strongman Alexander Lukashenko in last year's presidential vote BELTA / Oksana MANCHUK

Prosecutors had requested a 15-year sentence, the maximum possible punishment. Babaryko denied any wrongdoing throughout his trial.

The sentence is not subject to appeal.

Babaryko was also fined the equivalent of about 45,000 euros ($53,000) and barred from holding senior official positions.

Seven other defendants in the case, including several Belgazprombank executives, were also prosecuted.

They all pleaded guilty and on Tuesday were sentenced to terms of between three and six years.

Several key opposition figures were arrested in Belarus last year ahead of the presidential vote, clearing the way for Lukashenko, 66, to secure a sixth term.

Lukashenko's only rival was Tikhanovskaya, a political novice who took the place of her jailed husband in the vote and quickly gained popularity.

The leader of Babaryko's presidential campaign, Maria Kolesnikova, and his lawyer Maxim Znak are also in custody and have been charged with "conspiracy to seize power".

Despite Lukashenko's proclaimed victory, the opposition believes Tikhanovskaya was the true winner and that the vote was rigged.

Tens of thousands took to the streets of Belarus for weeks to protest the result but were met with a harsh police crackdown.

The authorities have also clamped down on independent media, jailing journalists over their coverage of the protests and withdrawing accreditation from foreign outlets.

Western powers have responded with a wave of sanctions against Lukashenko's regime.

They were toughened even further after a Ryanair passenger flight between European capitals was grounded in late May in Minsk and authorities detained opposition activist Roman Protasevich and his girlfriend who were on board.