Tymoshenko's lawyer has told the media guards at the Kharkov penal colony had beaten Tymoshenko as they forcibly moved her to a hospital from the penal colony on April 22.
"It is outrageous that Tymoshenko may have been beaten to force her to go to a hospital against her will," Hugh Williamson, Europe and Central Asia director at Human Rights Watch, said in a news release. "These allegations should be investigated and anyone responsible for ill-treatment should be prosecuted."
The guards, the lawyer said, twisted Tymoshenko's arms and legs and hit her in the stomach, causing her to faint. At a hospital, she refused recommended treatment for spinal problems, saying it was inappropriate.
HRW said a representative of the office of the Ukrainian ombudsman who visited Tymoshenko had documented injuries consistent with physical abuse, including bruising on the upper body and abdomen. The office also asked the State Penitentiary Service of Ukraine to provide medical treatment for Tymoshenko's spinal problems.
The State Penitentiary Service denied allegations of mistreatment, while the district prosecutor's office confirmed Tymoshenko was moved to the hospital against her will but said force used by guards was justified and complied with Ukrainian law.
Meanwhile, Tymoshenko's husband, Alexander, who lives in Prague, has asked her in a letter posted on her Web site to end the hunger strike she began April 20 after the alleged beating, ITAR-Tass reported.
Tymoshenko's daughter Yevgenia said Monday she had visited her mother in the penitentiary.
"My mother is very weak; her physical condition has deteriorated," the daughter said.
Tymoshenko, who served as prime minister from December 2007-March 2010, was sentenced to seven years in prison in October for abuse of office in the 2009 signing of Russian gas contracts.
Her conviction has been condemned as politically motivated by the United States, Russia, the European Union and human rights groups.
Tymoshenko, who lost an election to Viktor Yanukovych in 2010, has denied wrongdoing and claimed the charges are politically motivated.