KIEV (REUTERS) - Ukrainian President Viktor Yanukovich has gone on sick leave with a respiratory ailment, his website said on Thursday, with the issue of a new prime minister still undecided.

"The president of Ukraine has been officially registered as sick with an acute respiratory ailment and a high temperature," the web site said.

Mr Yanukovich's prime minister Mykola Azarov resigned on Tuesday in the midst of mass street unrest and the president has yet to appoint a successor.

Mr Serhiy Arbuzov, who was Mr Azarov's first deputy, has stepped in as interim prime minister.