Former Ukrainian Prime Minister Yulia Tymoshenko could face an even lengthier jail sentence after the Ukrainian Security Service completed a pretrial probe into her case Friday, report Ukrainian media, according to RIA Novosti.

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

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.

The security service withdrew the criminal case regarding the concealment of currency proceeds on January 18 as the offence was removed from the Criminal Code. Meanwhile, it will continue investigating other crimes Tymoshenko has been accused of.

Tymoshenko’s supporters believe the prosecution is politically motivated, an accusation the Ukrainian authorities deny.