German Finance Minister Wolfgang Schaeuble urged the new Greek government on Sunday to use a four-month extension it obtained for its financial rescue to implement its reform plan if it wanted to secure future help from abroad.

Last week Greece sent a list of reforms it plans to implement by the end of June to the Eurogroup of euro zone finance ministers, which then approved it, opening the way for the extension of the bailout.

Schaeuble told German television channel ARD that he had no guarantees that Athens would conduct reforms during the respite.

"But I hope they do it in the interests of Greece and also out of responsibility for Europe. But mainly in their own interests. Greece really needs to know that if it wants aid, it needs to keep the agreements it has made," he said.

On Saturday Greece called into question a major debt repayment it must make to the European Central Bank this summer, acknowledging it faces problems in meeting its obligations to international creditors.

But Schaeuble said: "If (the finance minister) doesn't make the first payment on time, that's a so-called default and I wouldn't want to be in his shoes bearing responsibility for what would then happen to Greece."

Schaeuble said Athens would get funds in the summer if the government met the conditions it agreed to, adding: "But if that's not the case then it won't be paid. That lies solely in the hands of those in positions of responsibility in Athens."

Germany's parliament ratified the extension of Greece's bailout on Friday, but Greece provoked anger in Berlin by saying Athens used "creative ambiguity" to win the loan lifeline from its partners.

Schaeuble said Friday's decision had not been easy for some of his colleagues, adding: "If we're then told, at the same time, that they didn't actually mean everything they said, that's not a very considerate way to behave towards us."

But he said that the agreements Athens had made were more important than the rhetoric coming from Greece.