The European Court of Human Rights on Tuesday ruled that Ukraine's detention of former prime minister Yulia Tymoshenko was unlawful but threw out accusations of ill-treatment.
"The Court considered that the detention had been arbitrary and unlawful during the entire period," the judges of the Strasbourg-based court said.
The judges also found that "the lawfulness of her detention had not been properly reviewed" by the Ukrainian judiciary "and that she had no possibility to seek compensation for her unlawful deprivation of liberty."
Responding to complaints by the jailed ex-premier over alleged ill-treatment during her transfer to hospital last year, the judges found there had been no violation of the European convention on human rights.
Tymoshenko's daughter hailed the EU court ruling as a 'first victory'
Speaking shortly after the ruling, Tymoshenko's lawyer urged Ukrainian President Viktor Yanukovych to immediately release his client, who has been detained since August 2011.
"I urge president Yanukovych not to appeal this decision and to instead follow this ruling. The only thing left to do now is to free Mrs Tymoshenko immediately," he said.
"The president is afraid of Mrs Tymoshenko because she is the only politician capable of defeating him in any election. That's why she is in prison," he said.
Both parties have three months to appeal the ECHR ruling.
European officials have said that Tymoshenko's release was a key objective as the bloc reviews ties with Ukraine and the possible signing of an association and trade accord.
The European Commission will deliver a recommendation to EU national governments in May on whether to sign the association accord.
Tymoshenko, who lost a disputed presidential election to Yanukovych in 2010, was jailed for seven years on what she says are trumped up charges of overstepping her authority while premier by agreeing a gas deal with Russia.