Newly elected Speaker of Parliament Oleksandr Turchynov speaks during a session of the Ukrainian Parliament in Kiev, Ukraine, 23 February 2014. Ukraine's parliament voted to appoint its speaker Oleksandr Turchynov as interim president and he will temporarily take over the duties of Viktor Yanukovych, whose whereabouts remained unknown.
Ukraine's acting president has assumed the duties of head of the armed forces.
Oleksander Turchinov's move was announced in a decree published on the presidential website Wednesday, Reuters reported.
Turchinov was assigned presidential powers by the parliament on Sunday. He is an ally of opposition icon Yulia Tymoshenko, the former prime minister who was convicted of abuse of office in a case widely seen as political revenge by her arch-foe Vitkor Yanukovych.
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Yanukovych has been on the run since being ousted as president last week. He has been accused of "mass killing of civilians" and the parliament on Tuesday voted to send Yanukovych to be tried by the International Criminal Court when he is caught. Yanukovych's whereabouts remain unknown.
Tymoshenko, the blond-braided and controversial heroine of the 2004 Orange Revolution, was ordered freed from prison by the parliament in the wake of clashes between anti-government protesters and police which left at least 80 people dead.
Elections are due to be held on May 25, with former boxing champ Vitali Klitchsko among the contenders.
Reuters and The Associated Press contributed to this report.