French President Nicolas Sarkozy, who is hosting the meeting in Cannes, said: "We said clearly to the Greek authorities that the EU, like the IMF, cannot envisage paying the sixth tranche until Greece has adopted the package and all uncertainty has been lifted.
"We cannot commit the money of taxpayers ... until the rules that were agreed on October 27 are respected. Without that, neither Europe nor the IMF can pay a single cent."
European leaders agreed a deal last Thursday that would see banks accept a 50% writedown of Greece's debt, higher than the 40% they had originally offered.
It would also increase the 440bn euro (£386bn) bailout fund to around 1trn euro (£876bn).
But Greek Prime Minister George Papandreou's decision to put the deal to the people sent stock and bond markets across the world falling.
Speaking after emergency talks with Sarkozy and German Chancellor Angela Merkel on Wednesday, Mr Papandreou said he was confident that his people would accept the EU bailout plan in the vote set for December 4.
"I believe the Greek people are wise and capable of making the right decision for the benefit of our country," he said.
"We are part of the eurozone and we are proud to be part of the eurozone."
Some of Greece's ministers said they had expressed reservations about the referendum but decided to support the government ahead of a key confidence vote expected in parliament on Friday.
Ms Merkel made it clear that, although she wished Greece would remain in the eurozone, the outcome of the referendum, whatever the question, would affect whether it was able to stay in the bloc.
"The euro as a whole must remain stable. We would prefer to ensure this with Greece rather than without it. But the top priority is stability," she said.
Mr Sarkozy's office said several eurozone leaders attending the G20, including the Spanish and Italian prime ministers, would meet on Thursday morning in Cannes to review the situation.
Major Asian economies warned Europe to tackle the crisis before it has a serious impact on economies elsewhere in the world.
China's deputy finance minister Zhu Guangyao said: "Like our European friends, we did not expect the Greek (call for a) referendum. It was an independent decision taken by Greece. I hope this period of uncertainty would be contained."
The White House said US President Barack Obama wanted "unanimity of purpose" to emerge from the G20 and White House spokesman Jay Carney said the situation would be a key subject.
