A Ukrainian court has opened preliminary hearings into former prime minister Yulia Tymoshenko's appeal of her seven-year jail sentence — without Ms. Tymoshenko at the proceedings.

She is appealing her conviction last month for exceeding her power as prime minister when she signed a 2009 gas deal with Russia that her opponents say was overly beneficial to Moscow — a charge she has denied.

However, the jailed former prime minister was not able to attend Thursday's hearing due to ill health. There has been growing alarm regarding her health since Monday, when Ukrainian Human Rights chief Nina Karpacheva said the former prime minister was suffering from serious medical problems and should receive treatment outside of prison.

Ms. Tymoshenko is suffering from a back problem, which she says authorities are refusing to properly diagnose and treat. Alexander Turchinov, the deputy head of Ms. Tymoshenko's All Ukrainian Union party, says Ms. Tymoshenko continues to feel worse.

Earlier this week, Ukrainian President Viktor Yanukovych promised to allow the jailed former prime minister to receive medical attention outside of the Kyiv prison after being informed the prison health care system is not up to the required standards. He also instructed authorities to provide Ms. Tymoshenko with medical care and attention that meet “European” standards.

Ms. Tymoshenko has denied the charges against her and described her trial as “a political lynching” aimed at allowing President Yanukovych to rid himself of a political rival. She had been expected to be the main opposition candidate in a parliamentary election next year, but is not eligible to run if the conviction is upheld.

Ukraine also has charged Ms. Tymoshenko in a separate case with embezzlement and tax evasion while she headed energy firm United Energy Systems of Ukraine in the 1990s.

The United States, the European Union and several human rights groups have condemned the charges against Ms. Tymoshenko as politically motivated.