Former Ukrainian Prime Minister Yulia Tymoshenko can face a longer jail sentence after the Ukrainian Security Service completed a pretrial probe into her case last week, RIA Novosti reported.

“The investigation will be carried to its conclusion and there will be a public trial,” Ukrainian Deputy Prosecutor General Yevgeny Blajivsky said.

Blajivsky also stated that investigators have proven that Tymoshenko managed the United Energy Systems of Ukraine (UESU) even after 1997, although her supporters insist that she did not.

"The investigation has enough evidence to prove its case," he added.

Tymoshenko was sentenced to seven years in prison in October for abuse of power after signing gas deals between Ukraine's Naftogaz and Russia's Gazprom in 2009. In late December she was taken to a penal colony prison.

Following the initial charges, she has also been charged with attempted embezzlement of public funds, organizing non-disclosure of foreign currency proceeds amounting to more than $165 million, and tax evasion amounting to over $5.8 million.