After a tumultuous week that left scores dead and Ukraine's political destiny in flux, fears mounted that the country could split in two - a Europe-leaning west and a Russian-leaning east and south.
Parliament arranged the release of Yanukovych's arch-rival, former Prime Minister Yulia Tymoshenko, who was on her way to Kiev to join the protesters.
Asked by crowds gathered at the hospital where she was released about her further plans, Tymoshenko said, "I will run for president," news agencies reported.
She said she will "make it so that no drop of blood that was spilled will be forgotten."
Yanukovych said he would not recognize any of the lawmakers' decisions as valid. He left Kiev for his support base in the country's Russian-speaking east, where lawmakers questioned the legitimacy of the newly empowered legislature and called for volunteer militias to uphold order.
"They are trying to scare me. I have no intention to leave the country. I am not going to resign, I'm the legitimately elected president," Yanukovych said in a televised statement, clearly shaken and with long pauses in his speaking.
"Everything that is happening today is, to a greater degree, vandalism and banditry and a coup d'etat," he said. "I will do everything to protect my country from breakup, to stop bloodshed."
Ukraine, a nation of 46 million, has huge strategic importance to Russia, Europe and the United States.
The country's western regions, angered by corruption in Yanukovych's government, want to be closer to the European Union and have rejected Yanukovych's authority in many cities. Eastern Ukraine, which accounts for the bulk of the nation's economic output, favors closer ties with Russia and has largely supported the president. The three-month protest movement was prompted by the president's decision to abort an agreement with the EU in favor of a deal with Moscow.
"A dictator has been overthrown," said protester Anatoly Sumchinsky, among thousands gathered on Kiev's Independence Square cheering a huge screen broadcasting a parliamentary debate. "We stood for our right to live in a different Ukraine. It's a victory."
Tymoshenko, the blond-braided icon of Ukraine's 2004 Orange Revolution, was heading from prison in the eastern city of Kharkiv straight to the protest camp, her party said.
Tymoshenko served 2½ years on a conviction of abuse of office that domestic and Western critics have denounced as a political vendetta. Tymoshenko's reappearance on the political scene could shake things up even more.
Saturday's developments were the result of a European-brokered peace deal between the president and opposition.
But Yanukovych said Saturday that he would not sign any of the measures passed by parliament over the past two days as a result of that deal. They include motions:
-saying that the president removed himself from power.
-setting new elections for May 25 instead of next year.
-trimming the president's powers.
-naming a new interior minister after firing the old one on Friday
The decisions were passed with large majorities, including yes votes from some members of Yanukovych's Party of Regions, which dominated Ukraine's political scene until this week but is now swiftly losing support.
Russia came out Saturday firmly against the peace deal, saying the opposition isn't holding up its end of the agreement, which calls for protesters to surrender arms and abandon their tent camps.
Russian Foreign Minister Sergey Lavrov on Saturday called his German, French and Polish counterparts and urged them to use their influence with the Ukrainian opposition to stop what he described as rampages by its supporters. European officials urged calm.
Ukraine's defense and military officials also called for Ukrainians to stay peaceful. In statements Saturday, both the Defense Ministry and the chief of the armed forces said they will not be drawn into any conflict and will side with the people. But they did not specify whether they still support the president or are with the opposition.
The president was in the eastern city of Kharkiv, where governors, provincial officials and legislators gathered alongside top Russian lawmakers and issued a statement saying that the events in Kiev have led to the "paralysis of the central government and destabilization of the situation in the country."
Some called for the formation of volunteer militias to defend against protesters from western regions, even as they urged army units to maintain neutrality and protect ammunition depots.
Protesters claimed full control of Kiev and took up positions around the president's office and a grandiose residential compound believed to be his, though he never acknowledged it.
At the president's office in central Kiev, a group of protesters in helmets and shields stood guard. No police were in sight.
Protesters also gathered around the country, often taking out their anger on statues of Soviet founder Vladimir Lenin, using ropes and crowbars to knock them off pedestals in several cities and towns. Statues of Lenin still stand in cities and towns across the former USSR, and they are seen as a symbol of Moscow's rule.
The past week saw the worst violence in Ukraine since the breakup of the Soviet Union a quarter-century ago. At the protests' epicenter on Kiev's Independence Square, demonstrators clashed with police and snipers opened fire. The Health Ministry put the death toll at 77, and some opposition figures said it was even higher.
At the square Saturday, protesters heaped flowers on the coffins of the dead.
"These are heroes of Ukraine who gave their lives so that we could live in a different country without Yanukovych," said protester Viktor Fedoruk, 32. "Their names will be written in golden letters in the history of Ukraine."
Dalton Bennett in Kharkiv, Angela Charlton and Jim Heintz in Kiev and Vladimir Isachenkov in Moscow contributed to this report.