Yulia Tymoshenko, Ukraine's former prime minister, has gone on trial for alleged abuse of power in a case she has dismissed as a political vendetta.
Tymoshenko denounced the hearing as an arranged "farce" orchestrated by Viktor Yanykovych, the president,
and told the judge he was a Yanukovich "puppet".
"At such an important moment for Ukraine, I do not want in that chair a judge like you. I am throwing down this objection to you because I consider you a puppet of the presidential administration," she told judge Rodion Kyreyev.
One of the leaders of the pro-Western Orange Revolution in 2004, Tymoshenko narrowly lost out to her old rival Yanukovych in presidential elections last year, becoming his fiercest critic.
She is now the target of several investigations, including for abuse of power that allegedly caused severe financial losses for Ukraine after the country's row with Moscow over Russian gas deliveries in early 2009.
Outside the court she told reporters: "This mock trial was organised and served up by Viktor Yanukovich. Nobody has any doubts that the courts and the state prosecution are in private hands and there will be no justice."
The hearing was adjourned until Saturday.
Tymoshenko is accused of causing a loss to the former Soviet republic's budget of $190m when she signed a new energy contract with Vladimir Putin, the Russian prime minister, after a brief interruption of gas deliveries two years ago.
The charges carry a sentence of between seven and 10 years, jeopardising Tymoshenko's ability to take part in parliamentary polls next year and the next presidential elections in 2015.
Analysts have previously said that it was not in the Yanukovych administration's interests to jail Tymoshenko as a new jail term would reinforce her image as a martyr.
"I have a feeling that a political decision has been taken to avoid giving her a suspended sentence," Sergei Vlasenko, who is also a deputy in Tymoshenko's political party, told the AFP news agency.
Dubbed as the 'Gas Princess', the former premier was earlier briefly imprisoned on charges of forgery and gas smuggling. The charges, which she says were also politically motivated, were quashed in 2005.
Her party has demanded that the authorities provide live coverage of the trial on national television and called on supporters to gather for a rally outside the courtroom.
Earlier this week, Tymoshenko said she had filed a complaint to the European Court of Human Rights, saying she was a victim of political persecution.
Source: Al Jazeera and agencies