All Greek parties must commit to reforms agreed with international lenders, no matter who wins upcoming elections, or Athens puts at risk a second bailout programme it needs to avoid default, German Finance Minister Wolfgang Schaeuble said on Tuesday.

Greece must implement the agreed measures and reforms. And of course all Greek parties must agree to the measures and a new programme, independently of the upcoming elections, Schaeuble told reporters in Brussels.

Greece, where the sovereign debt crisis that has threatened the euro and shaken the world economy started, is due to hold snap elections, and its co-ruling conservative New Democracy party said on Tuesday it wanted the vote by April 8.

But Antonis Samaras, whose party shares power in the coalition government with technocrat Prime Minister Lucas Papademos, has slammed the current policy mix, saying it risks plunging Greece even further into crisis. He has not backed some of the austerity measures prescribed by international lenders.

Opinion polls show New Democracy getting about 30 percent of the vote, about twice as much as the second-placed Socialist party but not enough to win outright. That would leave Samaras two options - form a coalition with other parties or ask for a repeat poll in the hope of consolidating his victory.

On Monday, euro zone officials sent talks for a bond swap deal back to square one by rejecting a final offer from the country's bondholders.

Athens needs the deal within days to ensure funds from a 130 billion euro rescue plan drawn up by European partners and the International Monetary Fund arrive before 14.5 billion euros bond redemptions fall due in March. International lenders have made debt sustainability a condition for a second bailout programme.

Schaeuble's comments were in line with those made by Austrian Finance Minister Maria Fekter, who said earlier: We will only be able to finalise (the bailout plan for Greece) positively when the governing party and the other parties agree.

(Additional reporting by Dina Kyriakidou in Athens and John O'Donnell in Brussels; editing by Ron Askew)