(CNN) -- A judge on Saturday postponed the tax evasion court hearing of former Ukrainian Prime Minister Yulia Tymoshenko, who is serving a seven-year prison sentence following last year's conviction of abuse of authority.
Judge Konstantin Sadovsky postponed the hearing until May 21, ruling that Tymoshenko could not be tried in absentia, the Ukrainian State News Agency reported.
Tymoshenko did not attend the hearing because of "massive back pain," according to the news agency.
The judge's ruling follows reports that Tymoshenko was roughed up in prison.
The two-time prime minister said Tuesday she was beaten unconscious in prison last week, but the prosecutor said his office investigated her claim and found no proof to substantiate her allegations.
But EU foreign policy chief Catherine Ashton said Tymoshenko's claim had been confirmed by the Ukrainian Ombudsperson's Office.
Tymoshenko was "subjected to physical violence during the transfer from her cell to a hospital on 20 April," read a statement released Thursday by Ashton's office
Ashton called on Ukraine "to examine promptly and impartially any complaints of torture or other forms of cruel, inhuman or degrading treatment," according to the statement.
Tymoshenko went on a hunger strike after the beating to draw attention to "violence and lack of rights" in her country.
Ashton's statement said she is "seriously concerned" about Tymoshenko's hunger strike. She asked Ukraine to allow the EU ambassador and independent medical specialists to visit the former prime minister in prison.
Tymoshenko said she was discussing with officials a transfer to a hospital for health reasons before the beating.
In a statement, Tymoshenko said that after her cell mate left the cell, "three sturdy men" entered, threw a bed sheet over her, dragged her off the bed and applied "brutal force."
"In pain and despair, I started to defend myself as I could and got a strong blow in my stomach through the bed sheet," she said in a statement.
Tymoshenko was dragged "into the street," she said. "I thought these were the last minutes of my life. In unbearable pain and fear I started to cry and call out for help, but no help came."
She fell unconscious, and when she came to, she was in a hospital ward, she said.
Last October, a Ukrainian court found Tymoshenko guilty of abuse of authority for signing overpriced gas contracts with Russia and sentenced her to the seven-year prison term.
The prosecutor said the gas deals inflicted damages to the country amounting to more than 1.5 billion hryvnas (almost $190 million at the current exchange rate). The court ruled she must repay the money.
Amnesty International has slammed the verdict as "politically motivated" and called for the release of Tymoshenko, who was prime minister from January to September 2005 and December 2007 to March 2010.
CNN's Zarifmo Aslamshoyeva contributed to this report.