(new info in lead, grafs 2-3, new video))

The head of Greece's radical left party, Syriza, is meeting leaders of the country's mainstream parties in hopes of forming a coalition government.

A coalition deal seems unlikely Wednesday, a day after Syriza party leader Alexis Tsipras called for the New Democracy and socialist PASOK parties to reverse their position on spending reductions linked to the multi-billion-dollar bailout keeping Greece afloat.

Tsipras called Tuesday for a rejection of all austerity measures imposed under an international loan deal. He said the Greek people's vote in Sunday's election nullifies the international loan agreement.

Syriza won 52 of the 300 seats in parliament in Sunday's poll, second behind Greece's conservative New Democracy party.

New Democracy was thus given the first chance to form a unity government. But party chief Antonis Samaras said Monday he was unable to form one after rejections from party leaders.

Greek President Karolos Papoulias has since given Tsipras three days to form a ruling alliance.

If those talks fail, the party that came in third will get the mandate to gain a majority in parliament. No agreement could force new elections next month.

Nervous European leaders have maintained pressure on Greece to continue respecting the requirements imposed on Athens in return for more than $300 billion in two bailouts.

The bailout deal, struck in February with the European Union, the International Monetary Fund and the European Central Bank, aims to clear the way for Greece to return to financial markets by 2015.