A Ukrainian court has again delayed the tax evasion and embezzlement trial of former prime minister Yulia Tymoshenko.

A judge Tuesday set the next hearing for September 11 after the 51-year-old opposition leader cited her poor health and refused to appear in court in the eastern city of Kharkiv.

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Tymoshenko's trial has been delayed several times due to her treatment for chronic back problems.

State Prosecutor Maryna Kapynis told reporters the trial will not begin without a defendant.

“The law regulating criminal proceedings demands that the hearing of a criminal case be held only with a defendant appearing in person to take part,'' she said.

Tymoshenko has denied the charges, dating to the 1990s. She says they amount to a vendetta against her by President Viktor Yanukovych, who won a narrow victory over her in 2010 voting. She is already serving a seven-year sentence for abuse of office linked to a natural gas deal she brokered with Russia in 2009 while she was prime minister.

Tymoshenko's lawyer described Tuesday's adjournment as “another illegal postponement” of the appeal hearing meant to take place later this week.

Meanwhile, the European Court of Human Rights has scheduled an August 28 hearing to examine whether Tymoshenko's initial arrest and trial were legal. A conviction in the tax evasion case could keep her in prison even if the earlier charges are overturned.