The head of the eurozone's finance ministers has called on Greece to "stop wasting time" and engage in serious talks on reform, BBC reported.
At a meeting in Brussels, Jeroen Dijsselbloem said there had been little progress made since discussions two weeks ago.
European creditors want to approve a detailed list of reforms before they release any loans to Greece.
But, so far, Greece has only outlined a broad range of intended changes.
Mr Dijsselbloem said: "It is taking way too long. We have offered to support them, but that goes hand in hand with conditions."
He said no real talks had yet started, adding: "There has been no implementation, so we have to stop wasting time."
Greek Finance Minister Yanis Varoufakis is yet to respond to the comments. On Friday, he sent a letter to eurozone officials outlining seven planned measures for reform.
But at the Brussels meeting, officials indicated the letter was only a starting point and did not contain detailed figures.
Greece aims to save €200m (£140m) through public spending cuts, as well as streamlining bureaucracy and cracking down on tax evasion.
It needs to agree terms so that it will become eligible for more credit from the eurozone and the International Monetary Fund. This would in turn allow its banks to finance themselves from the European Central Bank.
