Former Ukrainian President Viktor Yushchenko began testifying on Wednesday morning in the trial of his one-time prime minister, Yulia Tymoshenko. Yushchenko made his way to the court through a side entrance, avoiding journalists. He was greeted with cries of "shame!" by Tymoshenko supporters. Tymoshenko is on trial on abuse of office charges in connection with a “disadvantageous” 2009 gas deal she signed with Russia while she was premier of the former Soviet republic. She faces 10 years behind bars if found guilty. Yushchenko rejected a claim by Tymoshenko that he had called back the Ukrainian delegation involved in gas talks with Russia in late 2008. Tymoshenko says that if he had not withdrawn the delegation - which she headed - there would have been no subsequent cut-off of gas supplies to Ukraine by Russian energy giant Gazprom. "I had no authority to withdraw the delegation," Yushchenko told the court. Currently Ukraine's leading opposition figure, Tymoshenko has denied all the charges against her, saying they are politically motivated.