KIEV, Ukraine — Abandoned by his own guards and reviled across the Ukrainian capital but still determined to recover his shredded authority, President Viktor F. Yanukovych fled Kiev on Friday night to denounce what he called a violent coup, as his official residence, his vast, colonnaded office complex and other once impregnable centers of power fell without a fight to throngs of joyous citizens stunned by their triumph.

While Mr. Yanukovych’s nemesis, former Prime Minister Yulia V. Tymoshenko, was released from a penitentiary hospital, Parliament found the president unable to fulfill his duties and exercised its constitutional powers on Saturday to set an election for May 25 to select his replacement. But with both Mr. Yanukovych and his Russian patrons speaking of a “coup” carried out by “bandits” and “hooligans,” it was far from clear that the day’s lightning-quick events would be the last act in a struggle that has not just convulsed Ukraine but has also expanded into an East-West confrontation reminiscent of the Cold War.

Ms. Tymoshenko, who was jailed by Mr. Yanukovych after losing the presidential election in 2010, was released Saturday evening from the hospital in eastern Ukraine where she had been held, her representatives said. Many Ukrainians — and virtually all of the pro-Western protesters — believe that her conviction was politically motivated and regard her as something of a martyr to their cause. Late Saturday she appeared on the stage in Independence Square in Kiev in a wheelchair and delivered a speech that was greeted by cheers and chants of “Yulia! Yulia!”