The authorities in Ukraine have denied former Prime Minister Yulia Tymoshenko was beaten up in prison last week and invited German doctors to examine her, BBC News reported.

Tymoshenko, who is serving seven years in jail for abuse of office, has said she was attacked while being moved to hospital for an examination on Friday, April 20. Her lawyer says she has been on hunger strike since the alleged attack.

Tymoshenko's conviction over a gas deal with Russia was condemned in Western states as politically motivated. The former leading figure in the "Orange Revolution" has accused Ukrainian President Viktor Yanukovych, her old political enemy, of seeking revenge and the issue has overshadowed talks on co-operation between Ukraine and the EU.

Tymoshenko, 51, was moved from her prison to a hospital on Friday, then returned there on Sunday after she refused treatment for back pain.

In a statement, Tymoshenko accused three members of staff at the prison in the eastern city of Kharkiv of assaulting her while taking her to the hospital.

"They approached my bed, put a sheet over me and started dragging me off the bed, using brute physical force," she wrote.

"In pain and desperate, I started defending myself the way I could and received a strong fist punch in the abdomen," she said, her words read out to reporters by lawyer Serhiy Vlasenko. "They twisted my arms, lifted me up and dragged me outside wrapped in a blanket. I thought those were the last minutes of my life." Her lawyer said she had bruises on her arms and stomach.

But Ukrainian prosecutors denied the allegations and accused Tymoshenko of staging a political provocation designed to further damage relations with the EU.