Germany rejected Sunday calls to give Greece more time to implement economic reforms, with the economy minister saying in an interview that Athens needs to respect the bailout deal reached with its international creditors.

Philipp Roesler's comments to ZDF public television came after a visit by Greek Prime Minister Antonis Samaras to Berlin on Friday, during which he told German Chancellor Angela Merkel his country needs "time to breathe" before it can make all the budget cuts and reforms demanded as part of its €240 billion ($300 billion) bailout packages.

"What the Greeks have asked for, half a year or two years, that's not doable," said Roesler, who is also the vice chancellor in Merkel's coalition.

He added that "time is always money" and all parties had agreed that additional funds for Greece weren't up for debate.

Roesler, the leader of Germany's pro-business Free Democratic Party, has long taken a hard line on Greece. Last month, he caused an outcry in Greece by suggesting the idea of the country leaving the 17-nation eurozone had "lost its horror."

Those comments appeared to put him at odds with Merkel, who has always insisted that Greece should remain in the euro.

But his latest views on the need for Greece to stick to the agreed time plan for reforms were echoed by German Finance Minister Wolfgang Schaeuble, who told a newspaper in comments published Sunday that "more time generally means more money and that quickly means a new (bailout) program."

On Saturday, French President Francois Hollande urged Greece to do more to show its commitment to reforms, and offered the country no immediate hope for relief from its current regime of painful austerity measures. Like Merkel, Hollande said further decisions on Greece need to wait for a report next month by the country's debt inspectors. 

Meanwhile, Der Spiegel reported Sunday that Merkel wants an EU "convention" to draw up a new treaty for closer European political unification to help overcome the bloc's sovereign debt crisis.

Germany, the European Union's biggest economy, has long argued for more national competences, including over budgets, to be transferred to European institutions but faces strong resistance from other member states.

Merkel hopes a summit of EU leaders in December can agree a concrete date for the start of the convention on a new treaty, Spiegel said.

The idea, which Spiegel said Merkel's European affairs adviser floated at meetings in Brussels, recalls the 100-plus strong convention of EU lawmakers set up in 2001 -- inspired by the Philadelphia Convention that led to the adoption of the U.S. federal Constitution in 1787 -- charged with the task of preparing a European constitution.

The charter that finally emerged was rejected by French and Dutch voters in 2005 and it became instead the basis of the EU's Lisbon Treaty, which is still in force today.