BERLIN (Reuters) - European Commission Vice President Valdis Dombrovskis urged the Greek government in a German newspaper interview to speed up its reform efforts and said this was an essential prerequisite for further aid payments.
"Greece is today undoubtedly one of biggest concerns in the euro zone," he said according to a pre-publication copy of an article due to be published in German newspaper Bild on Saturday.
"We've lost a lot of time. Now the negotiations are gathering momentum but we need to step on it. Only once Greece has completed the next step of the reform programme can the last aid payments flow."
He also called on Athens to strengthen reform efforts and said there had been failures in important areas: "There has been progress in some areas but Greece must do even more, especially in terms of consolidating public budgets and in terms of pensions and the labour market."
On Friday, Greek Prime Minister Alexis Tsipras said his government would not back down from its red lines in negotiations with its foreign lenders but said a deal must be reached soon following months of talks.
Dombrovskis said the European Commission was "open for individual changes on the agreed reforms" but the perquisite was that these changes "don't put a bigger burden on public budgets and that the negotiations are not one-sided and without consultation".
He said Greece needed to now suggest reforms "and not simply reject proposals".
He said Greece did not have much time left and that given the "serious" financial situation in Greece there is "every reason for haste".
Dombrovskis therefore warned the Greek government to finally put together a "credible and comprehensive list of reforms".
He rejected the option of a Greek exit from the euro zone, saying: "We're working solely on the basis of the scenario that Greece remains in the euro zone."
Asked if Greece could remain a member of the euro zone even if it became insolvent, he said: "The euro is irrevocable. The EU treaties are clear on that."
Reporting by Michelle Martin; Editing by Christian Plumb, Grant McCool