Eurozone finance ministers have suggested Greece should be given until 2022 to lower its debt-to-GDP ratio to 120%, but International Monetary Fund chief Christine Lagarde said the existing target of 2020 should remain.
"We clearly have different views. What matters at the end of the day is the sustainability of Greek debt so that the country can be back on its feet," Ms Lagarde said.
Beneath her sharp exchange with Eurogroup chairman Jean-Claude Juncker lies a rift over whether eurozone governments need to write off some of Greece's debt to make it manageable.
IMF officials have pressed for such a "haircut" while Germany, the biggest contributor to eurozone bailout funds, has rejected it as illegal.
German Finance Minister Wolfgang Schaeuble said the 2020 deadline was "a little too ambitious".
Chancellor Angela Merkel has signalled she wants to keep Greece in the eurozone but is determined to avoid losses for German taxpayers before a general election in September 2013.
Mr Juncker, who heads the group of eurozone finance ministers, said a meeting would take place on November 20, and officials said more negotiations could be needed the week after to nail down a deal. The delay leaves Athens scrambling to meet a €5 bil-lion bond repayment deadline on Friday.
Despite Greece approving a tough 2013 budget last week, which it hoped would meet conditions for the release of the next tranche of emergency loans, Ms Lagarde said more work was needed to cement the budget measures.