The European Court of Human Rights said the rights of former Ukrainian Prime Minister Yulia Tymoshenko were violated. She was sentenced in 2011 to seven years in prison after being convicted on charges she abused her power in a natural gas deal with Russian energy company Gazprom.
Tymoshenko helped lead the country's Orange Revolution. Her supporters say the government of Ukrainian President Viktor Yanukovych pressed the case for political reasons.
Stefan Fule, European commissioner for neighborhood policy, and Catherine Ashton, the foreign policy chief for the European Union, issued a statement saying the court's decision confirmed EU concerns about arbitrary detention and selective justice in Ukraine.
They said the Ukrainian government should consider Tymoshenko's situation, describing her as an opposition leader jailed after a trial that didn't meet international legal standards.
"Ukraine also needs to take urgent steps to remedy the systemic procedural shortcomings identified in this (court) ruling, as part of a comprehensive reform of the judiciary, to prevent recurrence of arbitrary decisions and allay concerns over the selective use of justice," they said.
The European court rejected Tymoshenko's claims that she wasn't treated properly by healthcare officials at a Ukrainian detention center.
The European Union said justice reforms in Ukraine are central to improved bilateral relations.