(CNN) -- Ukraine's high court rejected an appeal Wednesday by former Prime Minister Yulia Tymoshenko, who had challenged her conviction on charges of abuse of authority.
She is serving a seven-year prison sentence after she was found guilty of the charges in October.
A Ukrainian court said she signed overpriced gas contracts with Russia. The gas deals inflicted damages to the country amounting to more than 1.5 billion hryvnias (almost $185 million at the current exchange rate), the court said, ruling she must repay the money.
"I am disappointed to hear that Yuliya Tymoshenko's final domestic appeal against her October 2011 conviction has been turned down," David Lidington, British foreign office minister for Europe, said Wednesday. "The UK will continue to press Ukraine to end selective justice and to ensure that the opposition is able to participate fully in free and fair parliamentary elections in October."
Amnesty International 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.
At the time, U.S. Secretary of State Hillary Clinton also called for her release and that of other members of her government "and the restoration of their full civil and political rights."
State Department spokeswoman Victoria Nuland said Wednesday Washington was "disappointed by this decision" to reject Tymoshenko's appeal and urged the Ukraine government to let her go.
In April, Tymoshenko went on a three-week hunger strike to draw attention to "violence and lack of rights" in her country after she said she was beaten unconscious in prison.
The prosecutor said his office investigated her claim of abuse and found no proof to substantiate her allegations, but European Union foreign policy chief Catherine Ashton said in April that the Ukrainian Ombudsperson's Office confirmed the report.
Ashton called on Ukraine "to examine promptly and impartially any complaints of torture or other forms of cruel, inhuman or degrading treatment."
Clinton also expressed concern over her treatment, saying in May that photos released by the Ombudsperson's Office "further call into question the conditions of her confinement."
CNN's Alla Eshchenko contributed to this report.