Greek Prime Minister George Papandreou risks a new euro zone crisis with his shock announcement that he will put the bailout deal struck last week to a referendum.

Euro zone leaders agreed to hand Athens a second, 130-billion-euro bailout and a 50-percent write-down on its enormous debt to make it sustainable.

Papandreou, whose ruling Socialist party has suffered several defections as it pushes waves of austerity measures through parliament while protesters rally outside, said he needed wider political backing for the fiscal measures and structural reforms demanded by international lenders.

"If there was to be a referendum, we may reasonably conclude that they may not accept the austerity measures. We may conclude that it will bring the pack of cards tumbling down," Howard Wheeldon, senior strategist at BGC Partners in London, said.

Analysts said holding a referendum -- likely to be early next year and only Greece's second in almost 40 years -- was baffling, given that the latest opinion poll showed a majority of Greeks took a negative view of the bailout deal.

And the renewed uncertainty will be likely be an embarrasment for G20 leaders in France this week trying to coax China into throwing the euro zone a financial lifeline.          

Early reactions to the surprise move ranged from accusations that Papandreou was gambling with the country's future and predictions of default, to questions over the legality of the referendum and statements by lawmakers that a No vote would force his resignation and early elections.     

Nobel prize-winning economist Christopher Pissarides caught the mood of uncertainty: "It is difficult to predict what will happen to Greece if they reject it. It will be bad enough for the European Union and the euro zone in particular, but it will be far worse for Greece.     
"In the scenario of a 'no' vote Greece would declare bankruptcy immediately, they would default immediately. I can't see them staying within the euro," he said.

Finland's Europe Minister Alexander Stubb said the referendum would be a vote on Greece's membership of the euro. "The situation is so tight that basically it would be a vote over their euro membership," Stubb told broadcaster MTV3. 

Analysts were divided over whether Greek voters would accept the deal, but agreed that a damaging month or two of market volatility lay ahead while pollsters repeatedly took the Greek voters' pulse and European leaders looked on nervously.

"This is going to bring back volatility and uncertainty in the market and essentially erase all the efforts made by the EU to make a deal," said Kathy Lien, director of currency research at GFT Forex, New Jersey.

"... with 60 percent against it, getting this passed will be a challenge, if passed it will provide extreme relief but given the protests and opposition it will be very difficult."     

The immediate market reaction to the announcement was negative, the euro extending losses against the dollar and tumbling more than 2 percent to a session low.  European shares were seen opening around 1.1 percent lower, according to financial bookmakers.

Opposition New Democracy leader Antonis Samaras will visit President Karolos Papoulias on Tuesday to discuss developments and push for snap elections, party officials said.  - Reuters