He admitted that the aim was to keep Greece within the euro, but that Germany would not allow Greece to delay reforms.
Speaking to the Bild newspaper, the minister refused to rule out excluding Greece from the euro. “The Greeks have the choice – reforms within the eurozone or no reforms outside it. There is no third option,” he said.
German Finance Minister Wolfgang Schäuble also insisted Monday that Greece needed to stick to its bailout plan obligations regardless of its domestic turmoil.
"Whatever will happen, Greece has to stick to what has been agreed. With a new government, with an old government, with new elections or a referendum or not," Schäuble told a 'Future of Europe' conference at Tampere University in southwestern Finland.
He stressed, however, that eurozone leaders needed to "pay respect to the burden the Greek people have to take. It is not fair what is going on in the Greek society ... but we can't avoid it."
Rösler, also head of the junior coalition partners the Free Democratic Party (FDP), ruled out holding a referendum in Germany on sending more bailout money to Greece, saying the plebiscites on finance policy were not allowed in German law. However, he did not rule out a public vote on other issues.
“I could imagine a referendum on passing further powers to the EU,” he said.
Greece's Prime Minister George Papandreou agreed to step down to make way for a interim national unity government after a fraught set of negotiations on Sunday with his cabinet and the opposition.
German Chancellor Angela Merkel on Monday expressed her "respect" during a phone call with Greek Prime Minister George Papandreou for his decision to step down, her spokesman said.
"The chancellor, for her part, expressed her respect for the decision of the prime minister and, from her side, expressed thanks for the good cooperation," Steffen Seibert told reporters at a regular press briefing.
The extraordinary meetings in Athens took place over the weekend in a desperate effort to shore up Greece's internal political rift and save Greece's membership of the eurozone.
The head of Deutsche Bank Josef Ackermann said Greece must not be cut loose of the eurozone. “That is a solution that we shouldn't even be considering,” he told state broadcaster ARD on Sunday. “That would be a dramatic result. We have to keep Greece in the eurozone.”