(BERLIN) - The International Monetary Fund "torpedoed" a recent attempt by European Commission chief Jean-Claude Juncker to offer Athens a compromise proposal in tortuous debt talks, a German daily reported.

Citing a "negotiator" as its source, the Frankfurter Allgemeine Zeitung said there had been "tensions" between the EU Commission and the IMF in recent days as Greece and its creditors race against the clock to come up with a debt deal to avert a catastrophic default by Athens.

The compromise that Juncker wanted to present to Greek Prime Minister Alexis Tsipras would have allowed Athens to postpone some 400 million euros in pension cuts in return for making similar savings on military spending, the newspaper said in its Sunday edition.

But the IMF was opposed to any such "bartering", the source was quoted as saying in the report.

Tsipras meanwhile warned Greece on Saturday to prepare for a "difficult compromise" with its EU-IMF creditors, who are demanding tough reforms in return for unlocking the last tranche of desperately-needed bailout funds ahead of key deadlines at the end of the month.

Top eurozone officials upped the pressure on Friday, saying they were preparing the ground for an Athens default, which could see Greece crashing out of the eurozone.