The latest developments in the ex-Soviet nation's three-month political crisis came after protesters took control of Kiev's charred city centre and seized Yanukovych's lavish residence and official offices, in a day of dramatic twists and turns.
Yanukovych denounced the "coup" and branded his political foes as "bandits", comments that won firm support from his backers in Moscow.
But the balance of power swung firmly in the opposition's favour a day after Yanukovych and the opposition signed a Western-brokered peace pact designed to resolve Ukraine's bloodiest conflict since its independence in 1991.
One of her close allies said Tymoshenko was travelling directly to address the crowds on Kiev's iconic Independence Square -- occupied since Yanukovych's decision in November to spurn an agreement with the European Union in favour of closer ties with Russia.
More From This Section
"The dictatorship has fallen," Tymoshenko said in a statement released on her official website. "It fell thanks to those people who came out to defend themselves, their families and their country."
Ukraine's pro-Russian regime appeared on the verge of collapse as lawmakers passed a resolution stating that Yanukovych was "removing himself (from power) because he is not fulfilling his obligations".
But Yanukovych defiantly told a local television station in the eastern Ukrainian city of Kharkiv -- a pro-Russian bedrock of support -- that he would fight tooth and nail against the "bandits" trying to oust him.
"I am not leaving the country for anywhere. I do not intend to resign. I am the legitimately elected president," the 63-year-old leader said in a firm voice.
Yanukovych said with a hint of outrage that "everything happening today can primarily be described as vandalism, banditry and a coup d'etat.