KIEV, Aug. 16 - A high court in Ukraine on Thursday began hearing the appeal of opposition leader and former Prime Minister Yulia Tymoshenko, who is seeking to overturn her seven-year jail sentence for abuse of office.

Tymoshenko is currently being treated for a back condition in a state hospital and was not present in court.

The judges questioned Tymoshenko's five lawyers, who argued that she should be released because no crime had been committed, as dozens of her supporters shouted "Freedom to Yulia" outside the courtroom.

The judges also heard a representative of the state energy company Naftogaz and a prosecutor, who both called for the appeal to be rejected.

Judge Stanislav Mishchenko then adjourned proceedings until 10 am Tuesday, when the court is due to hear the opinion of a second prosecutor before giving a final ruling on the case.

Jailed since August 2011, Tymoshenko was sentenced in October to seven years for abuse of power as prime minister by signing a gas contract with Russia that Ukraine decided was against its interests at the time.

"There is no proof of Tymoshenko's guilt," her lawyer Serhiy Vlasenko told reporters after the hearing.

If the court does not release Tymoshenko, she will be able to refer the case to the European Court of Human Rights (ECHR) in Strasbourg, France. To do this, she must first have exhausted all the legal options in Ukraine.

"We hope to get the judgment on August 21, which will open the way for us to the European Court of Human Rights," said Vlasenko.

Tymoshenko has already appealed to the ECHR over the circumstances of her arrest and her treatment in a case that is due to be heard on August 28.

One of the leaders of the Orange Revolution in Ukraine in 2004, Tymoshenko has always condemned her prosecution as personal revenge on the part of President Viktor Yanukovych, elected in 2010.

The Tymoshenko case has prompted serious rifts between Kiev and the West, which sees it as a political trial and calls for the ex-premier's release.

The European Union has supported Tymoshenko, calling her case an example of selective justice and shelving key agreements on free trade and political association with Ukraine.

Meanwhile, the Ukrainian authorities have been seeking to put Tymoshenko on another trial, now for alleged tax evasion and embezzlement in 1990s. A court has recently decided to delay the hearing until September 11.

The second conviction could keep Tymoshenko behind bars even if the EHCR eventually rules in her favor.

The trial in Kharkiv for tax evasion and embezzlement going back to alleged offences in the 1990s has been put off several times since she has been unable to attend because of back trouble for which she is receiving hospital treatment.

Tymoshenko, who was moved from prison to a state-run clinic in May for treatment for a chronic back problem, has refused to attend all the previous hearings in the new trial. (afp/tl/ez)