The US has yet to endorse the new leader, but says "Mr Yanukovych is no longer actively leading the country".Meanwhile, UK Foreign Secretary William Hague and his US counterpart are due to meet in Washington later to discuss emergency financial assistance to Kiev.An arrest warrant has been issued for Mr Yanukovych, who has disappeared.Acting Interior Minister Arsen Avakov said a criminal case had been opened against Mr Yanukovych and other officials over "mass murder of peaceful citizens".There have been unconfirmed reports that Mr Yanukovych is in Crimea.InvestigationDozens of people were killed in clashes between anti-Yanukovych protesters and riot police last week.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.Interim leader Olexander Turchynov said he hopes to form a new coalition government by Tuesday.Former PM Yulia Tymoshenko, who was released from jail on Saturday, has ruled out becoming prime minister.Russia on Monday issued its strongest response yet to the ousting of Mr Yanukovych, questioning the legitimacy of the Western-leaning interim leadership.Prime Minister Dmitry Medvedev said they had conducted an "armed mutiny".In a sign of further tension, White House official Jay Carney said on Monday that although Mr Yanukovych "was a democratically elected leader, his actions have undermined his legitimacy, and he is not actively leading the country at present''.Unrest in Ukraine began in November when Mr Yanukovych rejected a landmark association and trade deal with the EU in favour of closer ties with Russia.UK Foreign Secretary William Hague has warned Ukraine faces imminent economic collapse without support from the international community.He is due to meet US Secretary of State John Kerry in Washington on Tuesday for talks on emergency financial support for Ukraine.The US has already said it was ready to give financial support to Ukraine to complement any future loan from the International Monetary Fund (IMF).Ukraine is facing bankruptcy and a promised loan from Russia is looking increasingly unlikely.Meanwhile, EU foreign affairs chief Catherine Ashton has been in Kiev to discuss financial and political support for Ukraine's new leaders.On Monday she visited Independence Square - the scene of deadly clashes between protesters and police - and held talks with Interim President Olexander Turchynov.Senior US officials join EU officials in Kiev on Tuesday to participate in two days of meetings with political, business and civil society leaders.Western leaders, including French President Francois Hollande and German German Chancellor Angela Merkel, have sent written appeals to Russian President Vladimir Putin to urge a peaceful transition in Ukraine.On Sunday, Ukraine's parliament reduced the official status of the Russian language by cancelling a law brought in by Mr Yanukovych.Crimea and some pro-Russian areas in the east have seen protests against the overthrow of Mr Yanukovych, sparking fears that Ukraine could be split apart by separatist movements.Thousands of people remain in Kiev's Independence Square, the Maidan.Mr Yanukovych was last reported seen in Balaklava on the Crimean peninsula on Sunday.The peninsula is an autonomous region where the majority of the population is ethnically Russian.21 Feb: leaves Kiev for Kharkiv on helicopter; stays overnight in state residence22 Feb: flies by helicopter to Donetsk airport; tries to leave on private jet but stopped by border guards; leaves by car for Crimea23 Feb: arrives in Balaklava, Crimea, and stays briefly in a private spa before making aborted attempt to reach Belbek airportDismisses most of his security detail; leaves Balaklava in a three-car convoy with some guards and ex-presidential administration head Andriy Kluyev(BBC)ANN.Az