International Monetary Fund chief Christine Lagarde on Sunday told Greek Prime Minister Alexis Tsipras that "we are still a good distance away" in negotiations for a debt deal for hard-up Athens.
It comes amid tense ties between Greece and the IMF, after WikiLeaks said the lender sought a crisis "event" to push the indebted nation into concluding talks over its reforms.
"My view of the ongoing negotiations is that we are still a good distance away from having a coherent program that I can present to our Executive Board," Lagarde wrote in a letter to the prime minister and made public by the IMF.
"I have on many occasions stressed that we can only support a program that is credible and based on realistic assumptions, and that delivers on its objective of setting Greece on a path of robust growth while gradually restoring debt sustainability."
The Greek government reacted strongly to the WikiLeaks report, saying it wanted the IMF to clarify its position.
"The IMF conducts its negotiations in good faith, not by way of threats, and we do not communicate through leaks," IMF managing director Lagarde said in her letter, adding that she was releasing the details of the text "to further enhance the transparency of our dialogue."
"I also look forward to any personal conversation with you on how to take the discussions forward," she added.
In July, Greece accepted a three-year, 86-billion-euro ($94 billion) European Union bailout that saved it from crashing out of the eurozone.
But the bailout came with strict conditions such as fresh tax cuts and pay cuts.
The IMF worked with the EU on two previous bailouts for Greece since 2010 but the Washington-based lender said it would not participate in the third rescue plan without credible reforms and an EU agreement to ease Greece`s debt burden.