Her statement seemed to confirm analyst expectations that she is digging in for a political standoff with her rival, Viktor Yanukovych, that could delay the transfer of power.
Preliminary results from the Feb. 7 ballot gave opposition leader Yanukovych a lead of just 3.5 percentage points.
International observers called the election free and fair, but no winner has been officially declared, and Tymoshenko has refused to concede defeat.
She said Saturday she had evidence of fraud and would fight the result, for which the final count is to be announced on Wednesday.
“I have made the only decision I can make - to challenge the results in court,” said Tymoshenko, appearing stoical and resolute during the five-minute televised appeal to the public. “Not going to the courts today would mean leaving Ukraine to criminals without a fight.” She asked Ukrainians to support her legal battle to overturn the elections, but urged them not to take to the streets in protest as demonstrations would destabilize the country.
Responding to Tymoshenko's appeal, the deputy chairwoman of Yanukovych's Party of Regions said the legal challenge has no hope of success.
“She just wants to push us into a negotiation so that we will give her something. But we don't negotiate about democracy,” Anna German told The Associated Press. “This challenge only hurts the country's ability to begin reforms and deal with the financial crisis.” Tymoshenko helped lead the 2004 mass street protests against Yanukovych's election victory that year. Dubbed the Orange Revolution, those demonstrations on Kiev's central square, the Maidan, urged the Supreme Court to overturn Yanukovych's victory and call for a revote, which Tymoshenko's ally, Viktor Yushchenko, won by a narrow margin.
Yanukovych's team expected Tymoshenko to organize similar rallies in the streets this month, and thousands of his supporters have been gathered for days around the Central Election Commission to forestall such a move. But Tymoshenko said Saturday she would limit her fight to the nation's courts.
“I will not gather people on the Maidan, and will not allow a public showdown between citizens. Ukraine now needs stability and calm like never before,” she said.
Tymoshenko claimed more than one million votes had been falsified or miscounted, and she named the Russian-speaking Crimean peninsula - a Yanukovych stronghold - as the site of “shocking” irregularities.
The Central Election Commission said that, on Saturday alone, it had received 60 complaints from Tymoshenko's staff challenging the legality of the vote in numerous districts.
“I want to make it clear. Yanukovych is not our president, and he will never become the legitimately elected president,” she said.
Tymoshenko also claimed in her appeal that several observers from the Organization for Cooperation and Security in Europe, or OSCE, had agreed to support her legal challenge with “video evidence” in courts.
Officially, however, the OSCE has declared the elections “professional, transparent and honest” in a joint statement with other international observers.
Responding to Tymoshenko's claims, OSCE spokesman Jens-Hagen Eschenbaecher said he was not aware of any individual monitors' breaking ranks with the mission to support Tymoshenko.
“Officially, the mission will not support any of the candidates in court,” Eschenbaecher told the AP late Saturday, saying it is every candidate's right to mount legal challenges to the results. “This is part of the process.” The monitors' praise of the election conduct will likely hurt Tymoshenko's chances of mounting a successful court challenge.
Analysts said, however, that her legal complaints could discredit Yanukovych as he tries to consolidate power and repair the economy, which is still reeling from last year's steep recession.
“Challenging the results in court and delaying the final count will badly weaken Yanukovych,” political analyst Oleksiy Haran said. “Yulia is trying to chip away at his mandate and his legitimacy in any way she can.”
