The speaker of the Ukrainian parliament, the closest confidante of freed opposition leader Yulia Tymoshenko, has been temporarily handed the role of president following the ouster of Viktor Yanukovych.
Mr Yanukovych abandoned the capital yesterday, heading to his native east where he denounced what he called a "coup d'etat".
Parliament this morning voted to give Oleksander Turchinov, elected speaker on Saturday, Mr Yanukovych's duties as president.
The special parliamentary session was also told that a new unity government must be in place by Tuesday.
A presidential election has been set for May 25.
Mr Turchinov, 49, hails from the same city as Ms Tymoshenko, Dnipropetrovsk in southeastern Ukraine, and is deputy leader of her Fatherland party.
He served as head of Ukraine's state security service following the 2004-05 Orange Revolution that was co-led by Ms Tymoshenko.
The Ukrainian capital was calm overnight after a tumultuous day in which Mr Yanukovych was ousted from power, and several days of bloodshed which claimed 82 lives.
The exact whereabouts Mr Yanukovych is currently unknown
Local media reports say border police in the East prevented him from getting on a private jet to Moscow.
Barricades at Independence Square remain in place, and thousands of people remain on what is called the maidan listening to speeches, songs and religious ceremonies.
After her release from prison yesterday, Ms Tymoshenko hailed opposition demonstrators as "heroes" in an emotional speech in Kiev.
However, in a television interview conducted in the eastern city of Kharkiv, Mr Yanukovych said he would not resign or leave the country, and called decision by parliament to remove him "illegal".
"The events witnessed by our country and the whole world are an example of a coup d'etat," he said.
At Mr Yanukovych's abandoned estate a short distance from Kiev, people flocked to take photographs of his private zoo with ostriches and deer, replica ancient Greek ruins, and lavish waterways and follies.
EU Economic and Monetary Affairs Commissioner Olli Rehn said the EU was ready to offer "substantial financial assistance" once Ukraine had a new government.
"From a European point of view it is important that we provide a clear European perspective for the Ukrainian people who have shown their commitment to European values," Mr Rehn said after a meeting of the world's financial leaders in Sydney.
Russian Foreign Minister Sergei Lavrov said "illegal extremist groups were refusing to disarm and in fact are taking Kiev under their control with the connivance of opposition leaders".
The White House said Washington was keen to see the country build a new government and hold early elections and welcomed Ms Tymoshenko's release.