French President Nicolas Sarkozy said it could be held on 4 or 5 December.

German Chancellor Angela Merkel said the vote was over whether Greece wanted to stay in the eurozone.

Greek PM George Papandreou was summoned for crisis talks ahead of the G20 summit in Cannes to explain his surprise decision to call a referendum.

The move caused market turmoil on November 2, and had not been agreed with other European leaders.

The two-day meeting in Cannes of government heads from the Group of 20 major world economies formally begins on November 3.

.On November 2 evening US President Barack Obama left on an overnight flight to France aboard Air Force One. He is due to meet President Sarkozy first thing on Thursday morning.

Meanwhile, it has emerged that the UK is ready to support an increase in overall IMF funding for shoring up the euro.

However, a less-welcome development was China saying it could not commit to investing in the European Financial Stability Fund (EFSF) until the situation with Greece had been clarified.