In a telephone call about the unfolding crisis, Obama and Merkel "agreed that it was critically important to make every effort to return to a path that will allow Greece to resume reforms and growth within the eurozone," the White House said.
Obama and Merkel said their teams of economic advisors were closely monitoring the rapidly changing situation, the statement said.
Months-long bailout talks between Athens and its creditors dramatically broke down Saturday over the economic reforms demanded by creditors in exchange for more cash needed to keep Greece afloat.
Greek Prime Minister Alexis Tsipras stunned Europe late Friday with a surprise call for a July 5 referendum on the latest cash-for-reforms package and advised voters against backing a deal that he said spelled further 'humiliation'.
Greece's finance minister and the country's central bank chief were in crisis talks Sunday, weighing drastic banking restrictions to stave off a financial collapse as anxious Greeks emptied cash machines.
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