The US urged Greece to press on with reforms aimed at saving its floundering economy, warning that the failure to do so could result in "headwinds" for the global economy.
It is "important that the Greek government carries on" with reforms, White House spokesman Jay Carney told reporters.
"We're monitoring the situation and developments in Greece closely, and we are in regular communication with our European counterparts. We continue to believe that they have the capacity to deal with this," Carney said.
"So far, Greece has made significant progress in terms of reforms, but it is important that the Greek government carry on with the fiscal measures and reforms that are frequently under discussion with the EU and the IMF."
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His remarks came as Greek Prime Minister George Papandreou appealed for unity from his own lawmakers after two deputies quit and a growing number went public with their criticism of his plan to stave off bankruptcy.
In a dramatic address to his Socialist party, the embattled premier said that Greece and Europe as a whole were facing a pivotal moment in their history as he sought to nail down backing for an austerity package.
"The challenge before us, the moment we are facing, is historic. Either Europe will make history or history will wipe out the European Union," he said.
As a growing number of deputies went public with their criticism of the premier's plan to stave off bankruptcy, Papandreou urged "everyone to work together to overcome this crisis".
"We have some tough negotiations ahead of us and the next few days will be crucial ... These are critical moments for the country and we must have stability."
LAWMAKERS QUIT
Two other Socialist lawmakers, former deputy ministers George Floridis and Hector Nassiokas, quit their seats in protest at the government's economic policies and the failure of talks with the conservative opposition to form a national unity administration.
European Union meanwhile sought to buy time in order to cobble together a second bailout package for Greece, where the debt crisis threatens to place a huge strain on the euro.
The International Monetary Fund (IMF) had earlier said it was prepared to continue supporting Greece in its debt crisis, but only so long as Athens adopts agreed economic measures.
"We stand ready to continue our support for Greece subject to adoption of the economic policy reforms agreed with the Greek authorities," IMF spokeswoman Caroline Atkinson said in a statement.
The World Bank said it has no plan to join the international rescue of Greece, rejecting a suggestion by Mexico's central bank chief and candidate for the top job at the International Monetary Fund.
In response to a question about Agustin Carstens's comments, a World Bank spokesman said: "Our last loan to Greece was over 30 years ago. We have no intention of resuming lending."
Greece is classified among the "high-income countries" by the Washington-based development lender and effectively is expected to finance the World Bank, not borrow from it.
