Former Ukranian Prime Minister Yulia Tymoshenko, who has been freed by parliament after more than two years in prison, has addressed thousands of opposition demonstrators in central Kiev.
Earlier, parliament voted to remove President Viktor Yanukovych from office.
Sitting in a wheelchair, wiping away tears, Ms Tymoshenko praised the demonstrators who lost their lives in the street violence while protesting against the President.
"You are heroes," she told the crowd on Independence Square, the focus of protests against President Viktor Yanukovych.
The speech came at the end of a dramatic day, with the president fleeing Kiev but refusing to quit.
Ms Tymoshenko warned that the protesters should not think their job was done.
"Until you finish this job and until we travel all the way, nobody has the right to leave," she said. "Because nobody could do it - not other countries, nobody - could do what you have done. We've eliminated this cancer, this tumour."
But while she received large cheers from many in the audience, a BBC correspondent says she does not enjoy universal support among the opposition.
Before she went into prison in 2011, her popularity ratings were dropping and many Ukrainians blame her in part for the chaos of the post-Orange Revolution years, or see her as a member of Ukraine's corrupt elite.
The BBC reports that dozens of people walked away in disgust when she appeared on the stage, shouting that she did not represent them.
Ms Tymoshenko was freed following a vote by parliament on Friday paving the way for her release.
She was sentenced to seven years in jail after a controversial verdict on her actions as prime minister.
Earlier on Saturday, she left the hospital in the eastern city of Kharkiv, where she had been held under prison guard, and flew to Kiev.
Unclear who is governing Ukraine
Reuters reports it remains unclear who is governing Ukraine after a dramatic day in Kiev, with president Viktor Yanukovych fleeing the capital but refusing to quit.
The situation remains fluid and there's uncertainty over whether the opposition has triumphed, three months into the country's crisis.
In a brief television appearance earlier, Mr Yanukovych denied rumours he had resigned and denounced what he described as a coup.
His exact whereabouts is not known.
A bid by regional leaders loyal to him to challenge the legitimacy of the national parliament appears to have foundered, after thousands of protesters rallied in eastern Ukraine in support of the political changes in Kiev.
The meeting of governors of mainly Russian-speaking regions in the northeastern city of Kharkiv had raised the possibility of a split in the vast former Soviet republic of 46 million.
The leaders have denied this was their intention.