Ukraine's ex-prime minister Yulia Tymoshenko on Friday went on trial for alleged abuse of power, denouncing her rival President Viktor Yanukovych as a coward fearing political competition.

The former premier, known as the "Iron Lady," is accused of abuse of power in connection with a contract she signed with Russian Prime Minister Vladimir Putin after a brief interruption of gas deliveries from Russia in early 2009.

"Yanukovych is a coward. He is afraid of political competition and opposition," Tymoshenko, wearing a cream-colored suit and sporting her trademark golden braid wrapped around her head, told reporters.

She had earlier described the process as a "kangaroo court" and a vendetta orchestrated by the authorities.

"Whatever verdict is handed down, it will be a verdict against Yanukovych and not me," said Tymoshenko as several thousand supporters rallied in the streets near the courthouse in central Kiev.

Tymoshenko's family -- her businessman husband Olexander, daughter Yevgenia and son-in-law British hard rock musician Sean Carr -- turned up near the court in a show of support.

The stuffy courtroom was bursting at the seams from the volume of journalists and supporters and scenes of chaos occasionally interrupted the hearing.

Some shouted "Shame, shame on the entire Ukraine."

When the judge -- sweat dripping on his papers -- refused Tymoshenko's demand to recuse himself, her supporters yelled through a loudspeaker "shame on the judge."

Scores of police, some wearing anti-riot protective gear, ringed the courthouse.

After an initial hearing lasting a marathon nine hours, the judge adjourned the trial until Saturday.

One of the leaders of the pro-Western Orange Revolution in 2004, Tymoshenko narrowly lost to her old rival Yanukovych in presidential elections last year, becoming his fiercest critic.

She is now the target of several investigations.

One is for having allegedly caused a loss to the former Soviet republic's budget of 1.5 billion hryvnias ($190 million) when she signed a new energy contract with Putin after a brief interruption of gas deliveries in 2009.

The charges carry a sentence of between seven and 10 years in prison, jeopardising Tymoshenko's ability to take part in parliamentary polls next year and the next presidential elections in 2015.

Tymoshenko, holding a pink rose, entered the courtroom to cries of "Yulia, Yulia" and applause from her supporters.

Known for her penchant for theatrics, she crossed herself before the beginning of the pre-trial hearing and took a copy of the constitution, a small prayer book and an icon out of her handbag, putting them on the desk near her.

"This is a farce and circus and not a court hearing," Tymoshenko told the judge.

"The court system has been privatised by Yanukovych and his circle," she said, calling judge Rodion Kireyev the "presidential administration's puppet."

"They want to put me in prison but that will not help them. My voice will be stronger from prison than it is now and the whole world will hear it," Tymoshenko said.

Jose Manuel Pinton Teixeira, the EU's ambassador to Ukraine, who attended the trial together with a group of other foreign diplomats, strongly condemned the conditions of the hearing.

"I cannot give a political assessment of this case, but the conditions of this trial are inhumane," Teixeira told reporters as he headed out.

Tymoshenko signed a pledge not to leave Kiev but has not been detained so far in the investigation.

However several of her former top allies, including ex-interior minister Yury Lutsenko have been imprisoned in other investigations.

The United States, which has already raised concern of "selective prosecution" in Ukraine, criticised Friday's proceedings.

"When the senior leadership of an opposition party is the focus of prosecutions out of proportion with other political figures, this does create the appearance of a political motive," State Department spokeswoman Victoria Nuland said.

Critics say Tymoshenko has an insatiable thirst for power and revels in attention, even if it comes in the form of legal proceedings.

The former premier was previously briefly imprisoned on charges of forgery and gas smuggling. The charges, which she says were also politically motivated, were quashed in 2005.