Ukraine's interim leader Olexander Turchynov is due to form a unity government, days after the ousting of President Viktor Yanukovych.
Mr Turchynov said he hoped to form a new coalition government by Tuesday. Former Prime Minister Yulia Tymoshenko, who was released from jail on Saturday, has ruled out becoming PM again.
An arrest warrant has been issued for Mr Yanukovych, who has disappeared. In a Facebook post, acting interior minister Arsen Avakov said a criminal case has been opened against Mr Yanukovych and other officials over what he called the "mass murder of peaceful citizens".
MPs voted to remove Mr Yanukovych on Saturday after months of protest sparked by his rejection of a deal that would have brought Ukraine closer to the European Union. A crackdown on the protests last week left nearly 100 dead.
Mr Avakov says Mr Yanukovych has been seen in Balaklava on the southern Crimean peninsula, where 60 percent of the local population is ethnically Russian.
The United States has yet to endorse Olexander Turchynov, but says "Mr Yanukovych is no longer actively leading the country".
British investigators have told the BBC they are operating on the ground in Ukraine to help establish who was responsible for the most deadly day of violence last Thursday. They say they are gathering evidence which could be used to prosecute suspects.
Britain's Foreign Secretary William Hague and his American counterpart are due to meet in Washington to discuss emergency financial assistance to Kiev.
Russia has issued its strongest response yet to the turmoil in Ukraine and the ousting of the president. Prime Minister Dmitry Medvedev said the developments are a threat to Russian interests and its citizens, and the interim government has come to power as the result of what he calls an armed mutiny.
Moscow used similar language in 2008 when it poured troops into the breakaway Georgian republic of South Ossetia to protect its citizens there. Russia's ambassador has been withdrawn from Kiev.
Ukraine is facing bankruptcy and further promised loans from Russia are looking increasingly unlikely.
The United States administration's national security adviser, Susan Rice, has warned Russia against military intervention in Ukraine.
The US said it is ready to provide financial support to Ukraine to help it return to economic stability. A White House spokesperson says its support would help Ukraine make reforms and invest more in health and education.