Tymoshenko is serving a seven-year prison sentence after being convicted of charges that she abused her position of authority in 2009 when, as prime minister, she helped secure a deal with Russian gas company Gazprom.
Kiev claims that deal, which reopened natural gas flows following contract disputes, damaged a Ukrainian economy already battered by recession.
Tymoshenko lost a bruising 2010 campaign for president to Viktor Yanukovych and her Western backers believe the charges against her are politically motivated.
Yanukovych said during meetings with Lithuanian President Dalia Grybauskaite that his one-time ally wasn't the target of a political smear campaign.
"At a time when these crimes were committed, Tymoshenko was not the leader of the opposition," he was quoted by The National Radio Company of Ukraine as saying.
The European Parliament last week expressed frustration with Tymoshenko's conviction, saying that "Tymoshenko and other opposition leaders must be allowed to exercise their right to participate fully in the political process now, and in the future."
Tymoshenko was released from her prison cell briefly for medical tests. She's reportedly in grave condition with unspecified ailments.