Greece's conservative opposition leader has acknowledged he could not form a government and lambasted outgoing Prime Minister Alexis Tsipras for dragging the country back to elections after just seven months in power.

After a fruitless three-day search for a coalition partner, New Democracy leader Vangelis Meimarakis handed back a mandate to form a government to the country's president.

The baton now passes to the third largest bloc in parliament, the far-left Popular Unity party that broke away from Mr Tsipras's leftist Syriza party just last week with 25 lawmakers in the 300-seat chamber. The anti-bailout party is expected to be equally unsuccessful in putting together a coalition in the three days allotted to it, after which a caretaker government will be installed to arrange elections.