Germany is demanding that Greece sticks to its agreed bailout conditions after indications that Greece will to ask for more time to make cuts.
Foreign minister Guido Westerwelle says a softening of reforms is not possible.
Greek Prime Minister Antonis Samaras is to meet his German and French counterparts this week.
At issue is whether Greece has done enough to receive 31.5 billion euros in loans next month, which it needs to avoid a default.
Inspectors from the European Union, International Monetary Fund and the European Central Bank will publish a report next month on Greece, particularly its spending cuts, and efforts to raise revenue by clamping down on tax evasion and privatising state assets.