Ukrainian President Viktor Yanukovich has gone on sick leave with a respiratory ailment, his website said on Thursday, leaving a political vacuum in a country destabilised by anti-government protests.
Yanukovich's prime minister, Mykola Azarov, resigned on Tuesday after a sharp escalation of two months of street unrest prompted by Yanukovich's rejection of a European Union deal in favour of closer ties with Russia.
(Read more: Ukraine: Clashes as compromise deal rejected)
The president, under pressure from Moscow not to tilt policy back towards the West, has yet to appoint a successor. Serhiy Arbuzov, who was Azarov's first deputy, has stepped in as interim prime minister.
"The president of Ukraine has been officially registered as sick with an acute respiratory ailment and a high temperature," the web site said.
(Read more: Ukraine risks 'civil war': EU justice chief)
Yanukovich, 63, has not had a history of ill health. He has full control over the government and strong backing in parliament and analysts say he keeps his political cards close to his chest.
Ukraine badly needs a new government. Russian President Vladimir Putin said on Wednesday Moscow would wait until one was formed before fully implementing a $15 billion bailout deal. Anti-government protesters have occupied state buildings and fought street battles with police.