Greek Socialist leader Evangelos Venizelos called for a national unity government of all pro-bailout parties, but warned that forming such a coalition would be difficult.

In his first public comments since polls closed in Sunday's election, Venizelos said his PASOK party had paid the price for handling the country's sovereign debt crisis.

"For us in PASOK this day is extremely painful," he said. "We knew the price would be big but we decided to pay it. We embittered people to protect the nation's future.

"The possibility of a national unity government must be explored."

Unofficial results from the interior ministry show PASOK beaten into third place behind the conservative New Democracy and the anti-bailout Left Coalition.

New Democracy and PASOK together were seen taking less than 33 percent of the vote, giving them a combined one-seat majority in parliament at best.