A Ukrainian court has adjourned the tax evasion and embezzlement trial of former prime minister Yulia Tymoshenko until 11 September after she refused to appear, citing poor health.

The 51-year-old opposition leader is serving a seven-year sentence on a separate charge of abuse of office linked to a gas deal she brokered with Russia while prime minister in 2009.

Her trial in Kharkiv for tax evasion and embezzlement going back to alleged offences in the 1990s has been put off several times as she has been unable to attend because of back trouble.

She is receiving hospital treatment for the problem.

The court formally asked her this morning to agree to a video link from her hospital bed to enable the trial to take place. She has refused such a suggestion in the past.

Tymoshenko, the main political rival of President Viktor Yanukovich, has dismissed all charges against her as politically motivated.

She is challenging her initial conviction both locally and in the European Court of Human Rights.

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.

Tymoshenko led the 2004 Orange Revolution protests that derailed Yanukovich's first bid for presidency, and served twice as prime minister.

Mr Yanukovich, who beat her in a close run-off to become president in February 2010, has refused to intervene in Tymoshenko's prosecution despite being urged to do so by the EU.

A guilty verdict in the tax evasion case would keep Tymoshenko behind bars even if the European Court of Human Rights eventually overturns her first conviction.