All parties negotiating a new bailout for debt-strapped Greece agree that private creditors should be involved, but the details of how that would happen are still under discussion, Germany's finance minister said.

In an interview with the Saturday edition of Boersen Zeitung business daily, Wolfgang Schaeuble reiterated Berlin's position that financing a new bailout for Athens should not be left entirely to governments.

Fundamentally all parties agree that the private sector must do its part in a new Greek aid package -- but we are still discussing the 'how', he said.

We need a voluntary participation from private creditors, which firstly lends substantial support for Greece, second is quantifiable and third is reliable, he added.

The leaders of Germany and France, long at odds over how to involve private holders of Greek bonds in a new rescue package for Athens, said on Friday they agreed on a mild solution favored by Paris and the European Central Bank.

German Chancellor Angela Merkel said this approach, modeled on a 2009 agreement by banks to maintain their exposures in central Europe at the height of the financial crisis, was a good foundation for a Greek deal.

Bond markets remain fearful that Greece may default and most economists are overwhelmingly skeptical that it can ever repay its debt mountain, which has reached 340 billion euros ($480 billion) or 150 percent of the country's annual economic output.

Boersen Zeitung did not say when its interview was conducted and was not immediately available for comment by telephone.

(Writing by Brian Rohan; Editing by Ruth Pitchford)