Tymoshenko, who is serving a seven-year prison sentence after being convicted of abusing power while in office, released a video calling on citizens to throw out Yanukovych's ruling Party of Regions in the Oct. 28 elections, RIA Novosti reported Saturday.
"I want to appeal to all people: If you do not realize now that Ukraine is led by a criminal, that Ukraine is led by a mafia, then nothing can defend you from what will happen in a country led by Yanukovych," she said in the video, which was posted to her Fatherland party's website.
Tymoshenko said citizens must "overthrow the gang" and defeat the Party of Regions.
The opposition leader was convicted of criminally abusing her office while in power over natural gas import negotiations with Russia in 2009.
She denies all the charges and her supporters claim they are politically motivated.
Tymoshenko's lawyer recorded her statement on a cellphone Friday in a hospital where she is being treated for a herniated disc, Britain's Guardian reported.