(CNN) -- Former Ukrainian Prime Minister Yulia Tymoshenko, serving a seven-year sentence after last year's conviction on a charge of abuse of authority, has been on a hunger strike for four days because she was beaten unconscious in prison last week, she said Tuesday.
But the prosecutor said Tuesday that his office immediately investigated Tymoshenko's claim and didn't find proof to substantiate her allegations.
A medical expert was sent, but Tymoshenko refused an examination, said Gennady Tyurin, general prosecutor of Kharkiv region.
He said he has declined to open a criminal case.
"The investigation is over," Tyurin said.
Last October, a Ukrainian court found Tymoshenko guilty of abuse of authority for signing gas contracts with Russia and sentenced her to the seven-year prison term.
Prior to the alleged beating, Tymoshenko was discussing with officials a transfer Monday to a hospital for health reasons, she said.
But on Friday evening, her cell mate left the cell, and then "three sturdy men" entered, threw a bed sheet over her, dragged her off the bed and applied "brutal force," she said in a statement.
"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.
Tymoshenko went on her hunger strike the day after the beating, Saturday, she said.
She stopped taking food "to draw attention of the democratic world to things happening in the center of Europe, in the country named Ukraine," she said.
Tymoshenko charged that "the president of Ukraine is steadily and pedantically building a concentration camp of violence and lack of rights."
She is asking for a "public international investigation" into the administration of President Viktor Yanukovych and added, "we must do everything possible to remove the Yanukovych regime."
In April 2011, the Ukraine's Prosecutor General's office opened a criminal case charging Tymoshenko with signing overpriced gas deals with Russian energy provider Gazprom that inflicted damages to the country amounting to more than 1.5 billion hryvnas (almost $190 million at the current exchange rate) and that Tymoshenko had allegedly no right to sign.
The court ruled Tymoshenko must repay the money, and she is banned from holding public office for three years.
Tymoshenko narrowly lost to Yanukovych in a presidential election in February 2010, and she became his fiercest opponent.
She has repeatedly brushed off all charges against her as political, calling the trial a "farce" and naming the judge a "stooge of Yanukovych's administration," appointed to "fabricate" the case.
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 Michael Martinez contributed to this report.