KIEV, Ukraine - Ukraine's president on Wednesday defied renewed Western pressure to release jailed former Prime Minster Yulia Tymoshenko, a longtime political rival, by insisting he cannot interfere in the judicial process.

Tymoshenko, now the top opposition leader, was sentenced to seven years in jail in October on charges of abuse of office in a case that the European Union and the United States have condemned as politically motivated. The EU balked at signing a key co-operation agreement with Kyiv this week over her jailing.

President Viktor Yanukovych told reporters that he personally does not oppose Tymoshenko's release but that the matter was out of his hands.

"It is impossible to stop the investigation, it is impossible to stop court hearings ... nobody has the power to intervene in them. The system is independent, it is working," Yanukovych said in an end-of-the-year news conference.

"I would not be against her being released under certain circumstances, envisioned by the Ukrainian legislation," he said.

He added, however, that interfering in the legal process would be illegal. "It would also be a crime if I begin abusing my powers," he said.

Tymoshenko was found guilty of overstepping her authority while negotiating a natural gas import contract with Russian in 2009.

She maintains her innocence and charges that Yanukovych ordered her imprisonment in order to bar her from elections. She has also been charged and investigated in several other cases in recent weeks.

A Kyiv court is now hearing Tymoshenko's appeal of her sentence.