Tymoshenko is serving a seven-year prison sentence after being convicted of abusing her authority when, as prime minister, she helped broker a natural gas deal with Russia's Gazprom in 2009.
In an interview with Polish Newsweek from prison, Tymoshenko said her opposition All-Ukrainian Union "Fatherland" party was fighting an uphill battle against the administration of Viktor Yanukovych.
"The courts, the Central Election Commission, the district electoral commissions, the mainstream media are controlled by the regime," Tymoshenko said. "There has never been such fraud in Ukraine."
She maintained her opposition would do what it could to stand up to pro-Yanukovych groups but warned the chances "are small" without support from the European community.
A high court in Kiev last week rejected an appeal filed by Tymoshenko's defense team. Her counsel wanted the charges thrown out because of a lack of evidence.
Tymoshenko's attorneys said they'd take the case to European courts. The European Union said trials for opposition leaders in Ukraine haven't met international standards for "fair, transparent and independent legal processes."
Parliamentary elections in Ukraine are scheduled in October.