The German government softened its tone on Greece a day after its finance minister firmly rejected Athens' latest request for a bailout extension, saying that although the proposals needed work, they were a good basis for further talks.

Finance Minister Wolfgang Schaeuble surprised his European partners and German cabinet colleagues on Thursday by dismissing a letter from his Greek counterpart as a stealth attempt to win more aid without committing to agreed budget and reform targets.

But ahead of a crunch meeting of euro zone ministers in Brussels on Friday, Chancellor Angela Merkel distanced herself, through a spokeswoman, from the confrontational tone used by Schaeuble - while at the same time praising her minister and describing the government as fully united.

"The letter from the Greek finance minister makes clear that Greece remains interested in support from the European Union," Christiane Wirtz said. "This letter is a good signal which allows us to continue to negotiate."

She added that euro zone finance ministers meeting in Brussels on Friday would "continue to negotiate on this basis" and that the talks would "hopefully lead to an agreement with Greece."

Asked whether Merkel supported Schaeuble, a veteran 72-year-old conservative who has more leeway than other ministers to speak his mind, Wirtz said Schaeuble was doing an "excellent job in this crisis and in the negotiations with Greece."

His outright rejection of the proposals from Greek Finance Minister Yanis Varoufakis underscored the mistrust between Berlin and Athens that has developed since leftist Alexis Tsipras rode to victory in an election last month vowing to row back austerity measures favored by Berlin and its euro allies.

It prompted Tsipras to call Merkel on Thursday evening. They spoke for nearly an hour and although the German government declined to give details of their conversation, Wirtz said Berlin did not dispute Tsipras's description of the talks as constructive.

Greece's current bailout program runs out at the end of this month. If by then it has not clinched an extension, experts fear an acceleration of capital outflows would cripple its banks, triggering an unprecedented exit from the euro zone.

German magazine Der Spiegel reported on Friday that officials at the European Central Bank had begun preparing contingency plans for a so-called "Grexit."

While Schaeuble has made clear he believes the euro zone could weather such a step, Merkel and Germany's European partners may be more reluctant to take that risk.