Greek PM George Papandreou is facing a major challenge in his efforts to form a government of national unity to handle the country's debt crisis. His governing Socialist (Pasok) party narrowly won a vote of confidence on Friday night, which had placed a vital EU bailout in jeopardy. But the main opposition New Democracy party has said it would not join a coalition under Mr Papandreou. Party leader Antonis Samaras said Mr Papandreou must call snap elections. The prime minister's office says Mr Papandreou will meet President Karolos Papoulias at 12:00 (10:00 GMT) to announce his plans to form a government of national unity. Finance Minister Evangelos Venizelos said elections could be held once procedures for securing the EU bailout package were finished. The BBC's Mark Lowen in Athens says it is looking increasingly unlikely that Mr Papandreou will lead a coalition, with reports emerging that Mr Venizelos could be named as an interim prime minister. The prime minister has been fighting for his political life, facing calls for his resignation even from within his own party. Earlier this week he shocked EU partners and sent markets into turmoil after calling for a referendum on the hard-fought EU deal struck last month to great fanfare. Ministers later confirmed the referendum plan had been dropped but the confidence vote went ahead. The late-night vote was on a knife-edge, but the government eventually won with 153 votes to 145. During the hours of debate, Mr Papandreou said the bailout deal currently on offer by the EU had to be accepted, and it would be "historically irresponsible" to lose it. Immediate elections would be "catastrophic" for the deal, he said, so proposed a new, broad coalition to take charge until it had been agreed. "I therefore ask for a vote of confidence in order to ensure the security of this nation." Hinting that he might stand aside, he said he would not put personal ambition before saving the country. "I am not interested in any post, the last thing I am interested in is whether I am re-elected," he said. The prime minister's pledge to seek an interim government appears to have calmed a revolt among Pasok MPs. But Mr Samaras dismissed the prime minister's idea of a coalition government, saying Mr Papandreou had rejected his proposals. "The responsibility he bears is huge," he said. "The only solution is elections." Bankruptcy The confidence vote had been timed to take place when markets in Europe and the US were closed. Outside parliament, several thousand communist supporters staged a noisy rally, banging drums and waving red flags, while hundreds of riot police stood guard nearby. German Chancellor Angela Merkel's chief whip in the German parliament, Peter Altmeier, hailed the confidence vote as an important development. "It matters if they are able to form a cross-party government of national unity," he told the BBC's Newsnight. "That is what they should do and this government of national unity should engage in a... commitment to implement this reform package." The Greek debt crisis had dominated the agenda at the G20 summit in Cannes this week, where Mr Papandreou was summoned for urgent talks on Wednesday. European Commission President Jose Manuel Barroso acknowledged it was possible that Greece could end up leaving the eurozone, but said it was "in their interests" to stay. "I think the principle of a country leaving the euro is not a good one. But at the end, it depends on them being able to implement the decisions taken together," he said. The summit put the next tranche of Greece's existing bailout on hold. Without the bailout funds, Greece may go bankrupt before the end of the year. The leaders in Cannes also agreed to boost the resources of the International Monetary Fund (IMF) in an effort to support economic growth. The EU bailout deal, agreed last month, would give the heavily indebted Greek government 130bn euros (£111bn; $178bn) and it imposes a 50% write-off on private holders of Greek debts, in return for deeply unpopular austerity measures. Although the Greek public has strongly resisted the austerity measures, a recent opinion poll in a newspaper showed 70% wanted to remain within the eurozone.