Greece has told its European and International Monetary Fund creditors it cannot implement some of the extra changes sought in exchange for fresh bailout loans, three sources close to the talks said on Monday.
The move, if confirmed, could further delay the disbursement of the bailout funds which Athens badly needs to pay off IMF loans in June and European Central Bank bonds maturing in July and increasing state arrears.
Last week, after months of negotiations, Greece and its lenders concluded a key bailout review, opening the way for debt relief that Greece has long desired.
The lenders also gave the green light for the disbursement of 10.3 billion euros in tranches, on condition that Athens amends some recent laws concerning pensions, privatisations and freeing up the sale of bad loans.
But in a letter sent to the lenders last week, Finance Minister Euclid Tsakalotos said some of the additional demands could not be fulfilled, the sources said.
The finance ministry had no immediate comment and it was not immediately clear whether the release of the funds was at risk.
According to one of the sources, some of them were related to pension reforms.
"We cannot make any substantial changes. But we will proceed with the technical amendments discussed. Some of them are right," a government official told Reuters.
Greek newspaper Ta Nea said the letter was sent to EU Commissioner Pierre Moscovici, the ECB's Benoit Coeure and the IMF's Poul Thomsen.