Europe's debt drama has dominated talks among leaders of the Group of 20 leading economies in Cannes with Greece's government facing potential collapse.
European leaders admitted that the eurozone may face losing its weakest member.
US president Barack Obama said the most important task at the G20 summit is to resolve the European financial crisis and urged European Union leaders to flesh out details of their ambitious plan to rescue Greece and stabilise financial markets.
French president Nicolas Sarkozy scrambled to save the summit he is hosting from being hijacked by the tumult in Greece. Mr Sarkozy said he and Mr Obama agree the private sector should play a greater role in helping resolve the global financial crisis.
"We have found a common analysis to make the financial world contribute" to finding a solution to the crisis, Mr Sarkozy told reporters after talks with the president. He said he welcomed Mr Obama's "understanding on subjects such as a tax on financial activities".
Mr Sarkozy and some others in Europe have been pushing for a small tax on all financial transactions that could be used to help poor nations and reduce debts.
The Obama administration and several leading economists are cool to the idea, favouring instead fees on the biggest banks. Mr Obama said he and Mr Sarkozy discussed developments in Greece "and how we can work to help resolve that situation".
Mr Sarkozy is also welcoming Hu Jintao of China as well as the leaders of India, Brazil, Russia and the other members of the G20 in this city made famous by its annual film festival. But the event is far from the star turn the unpopular French leader had hoped to make six months before he faces a tough re-election vote.
European leaders held another round of emergency meetings about Greece, this time including officials from Spain and Italy - two major eurozone members whose debts have rattled markets and who are seen as too big for Europe to bail out.
All attention is on Greece, where the embattled Socialist government was on the point of imploding today as a revolt against prime minister George Papandreou's planned referendum on the country's hard-won international bailout package gathered pace.