The ex-Soviet state's three-month crisis culminated in a dizzying flurry of historic changes over the weekend that saw parliament sideline president Viktor Yanukovich and call a new presidential poll for May 25.
Lawmakers then went a step further by approving the release from her seven-year jail sentence of former prime minister Yulia Tymoshenko -- a star of the 2004 Orange Revolution who was thrown behind bars less than a year after Yanukovich came to power in 2010.
The constitutional legitimacy of parliament's actions remained an open question and Yanukovich vowed in a taped interview to fight the "bandits" who now claimed to rule Ukraine.
But Yanukovich's authority was nowhere in evidence in Kiev on Sunday. The city's police presence had vanished and protesters were in control of everything from traffic management to protection of government buildings after a week of bloodshed claimed nearly 100 lives.
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Yanukovich was dealt another blow when his own Regions Party condemned him for issuing "criminal orders" that led to so many deaths.
Parliament also voted to dismiss Ukraine's foreign minister Leonid Kozhara after sacking the federal police chief and prosecutor general on Saturday.
'Government of the people'
Lawmakers voted on Sunday to name close Tymoshenko ally Oleksandr Turchynov – himself only appointed parliament speaker on Saturday in place of a veteran Yanukovich supporter – as interim president tasked with forming a new government by Tuesday.
Turchynov immediately vowed to draw up a "government of the people" and warned Russia that he expected the Kremlin to respect his country's pivot.
"We are ready for a dialogue with Russia... that recognises and takes into account Ukraine's European choice," the 49-year-old said in a television address.
Both Washington and EU powers vowed to drum up aid that could pull Ukraine out of a crisis sparked in November when Yanukovich spurned an historic EU trade deal and later secured a $15-billion bailout pledge for the struggling nation from its old master Russia.
Russia once again warned that delivery of its huge bailout package was on hold.
Ukraine owes nearly $13 billion in debt payments this year -- money it cannot drum up on financial markets because of prohibitively expensive borrowing costs.
Turchynov warned on Sunday that Ukraine was "rolling toward an (economic) abyss".
US Treasury Secretary Jacob Lew told a G20 meeting in Sydney that Washington now "stands ready to assist Ukraine as it implements reforms".
EU foreign policy chief Catherine Ashton will fly to Kiev on Monday for a two-day visit that her office said will aim to work out "measures to stabilise the economic situation" in Ukraine.
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Fears of Russian tanks
The United States and Britain also took joint steps to halt any potential retaliation from the Kremlin following the swift and unanticipated fall of a leader who had been backed up personally by Russian President Vladimir Putin.
A senior US State Department official said Secretary of State John Kerry underscored by phone to Russian counterpart Sergei Lavrov that it was "the United States' expectation that Ukraine's... democratic freedom of choice will be respected by all states."
US National Security Adviser Susan Rice also bluntly warned Russia that sending in troops to restore a more Kremlin-friendly leadership in Kiev "would be a grave mistake".
Rice piled further pressure on Putin by telling NBC television that "this is not about the US and Russia."
"This is about whether the people of Ukraine have the opportunity to fulfill their aspirations and be democratic and be part of Europe, which they choose to be."
Britain's Foreign Secretary William Hague also stressed that "any external duress on Ukraine any more than we've seen in recent weeks... it really would not be in the interests of Russia to do any such thing."
But Hague, when asked about the possibility of Putin ordering tanks into Ukraine, said: "We don't know, of course, what Russia's next reaction will be."
Russia's anxiety about the fast-paced changes was underscored late on Sunday when the foreign ministry recalled ambassador Mikhail Zurabov "due to the escalation of the situation in Ukraine".
The Moscow ministry also said Lavrov had flatly told Kerry that Russia strongly condemned "the seizure of power" by the opposition in Kiev.
Read: Ukraine's opp leader freed, speaks to protesters
Tymoshenko for president?
The whereabouts of Yanukovich himself meanwhile remained a mystery amid speculation that he was hiding out in the pro-Russian east.
Ukraine's border service said the ousted president had been kept from fleeing the country out of the eastern city of Donetsk because his charter plane did not have the required paperwork.
But attention of world leaders was quickly shifting to Tymoshenko amid mounting speculation that the former premier had the best chance of uniting the opposition for a presidential bid.
Tymoshenko held telephone talks with Merkel and also met Western ambassadors in Kiev.
Her spokeswoman stressed that the 53-year-old -- charismatic but also dogged by allegations of corruption dating back to the 1990s -- had made no decision about running in May.
The opposition's main presidential challenge had been primarily expected to come from boxer-turned-lawmaker Vitali Klitschko.