Greek socialist leader Evangelos Venizelos met on Saturday with President Carolos Papoulias to return his mandate to form a cabinet, an AFP reporter said, making all-party talks the only hope to avert a new ballot.
Venizelos was the third party leader who tried and failed to cobble together a government after inconclusive elections on Sunday punished pro-austerity parties but failed to produce a clear winner.
Head of state Papoulias is now expected by Monday to urge party leaders to form a national unity government, a process that could take several days.
If the parties cannot agree a compromise by next Thursday, new elections will have to be called in June.
The country's international creditors have warned that no new loans will be forthcoming if it falters on structural reforms required to set the Greek economy to order after decades of overspending by the state.
But highly-indebted Greece is deeply torn over the tough austerity measures imposed as conditions for IMF-EU bailouts, and the crisis has raised the threat it could default and even leave the 17-member eurozone.© ANP/AFP