European leaders open a pivotal summit Thursday facing cranked-up demands led by the United States for a breakthrough on Greece amid fears its debt crisis will wreak havoc across Europe and beyond. Pressure increased on the 27 EU leaders to act when Greek unions announced a general strike next week timed to coincide with a crucial parliamentary vote on massive new spending cuts. Greece could default should Prime Minister George Papandreou lose the vote. Under calls from the International Monetary Fund and markets to resolve the 18-month crisis, German Chancellor Angela Merkel will meet French President Nicolas Sarkozy in the hours before the summit starts at 7:30 pm (1730 GMT). Papandreou, along with the chair of the Eurogroup finance ministers Jean-Claude Juncker, European Central Bank chief Jean-Claude Trichet and EU leaders Herman Van Rompuy and Jose Manuel Barroso will also attend. Eurozone leaders \'to hold talks with Greek PM\' The meeting could prove a defining moment for the European Union as the possibility of Greece exiting the shared euro currency area or even the entire bloc disintegrating are no longer taboo. \"The spectacle the Europeans have made of themselves in the face of the Greek crisis is an absolute disaster\" for the cause of post-WWII integration, warned respected analyst Jean-Dominique Giuliani of the Robert Schuman Foundation. Warning that Europe must act now, US Federal Reserve chief Ben Bernanke said on the eve of the talks: \"If there were a failure to resolve that situation, it would pose threats to the European financial systems, the global financial system and to European political unity. \"I think the Europeans appreciate the incredible importance of resolving the Greek situation,\" he said.