Jailed communist Mikhail Kononovich thanked supporters who have protested in solidarity with Ukrainian political prisoners as the trial of him and his brother Alexander resumed on Monday.
The brothers said that leftists are being persecuted in Ukraine for political reasons and praised those who held demonstrations in London, Madrid, Rome, Brussels and Belarus.
They face life in prison on charges of “actions aimed at seizing state power,” although little evidence has been presented to back the claims.
Mikhail Kononovich is the leader of the Leninist Communist Youth Union of Ukraine and was detained alongside his brother Alexander in March amid fears they were to be executed.
They were seen for the first time last month, handcuffed and allegedly suffering the effects of torture as intelligence services pressured them to confess to crimes they have not committed.
Despite appeals from the brothers, the international response has been muted, while the European Union has failed to respond to requests from the Greek Communist Party to assure their safety.
The brothers are ethnic Belarusians and Mikhail accused the Western-backed opposition leader Svetlana Tikhanovskaya of ignoring their plight.
“I want to address, as a Belarusian of Ukraine, to the so-called opposition, Tikhanovskaya, to those who are at the mercy of the West and the United States.
“Which Belarusians did you pull out of the dungeons of the Zelensky regime? Do you even know how many Belarusians are in prisons in Ukraine? How are you helping them?” he asked.
You run around Europe and the US, telling stories, asking them for money. Who exactly did you help?
He accused Ms Tikhanovskaya of hypocrisy for speaking out about those detained in Belarus while remaining silent over Belarusians jailed in Ukraine.
The trial of the Kononovich brothers opened earlier this month, however they have not been allowed to attend the court hearings, appearing via video-link.
They appealed to Western media outlets and members of the European Parliament to attend their “show trial” and witness it for themselves.
The Communist Party of Ukraine was permanently banned on July 5 while all of its assets, including property and funds, were seized by the state.
It was the 14th opposition organisation to be shut down by Ukrainian authorities who have also closed all but one media organisations in the country, which is government controlled.