She also reiterated her support for Britain's strong presence in the EU, despite Prime Minister David Cameron's move to block a new fiscal pact in December.
In the interview with the BBC's "Newsnight" TV programme on Monday, Merkel said: "Britain needs to know that we in Germany want a strong Britain in the EU, we always have and we always will."
She said Athens had a "long and arduous road" to recovery after being forced to seek two international rescue packages, but it would be a "huge political mistake to allow Greece to leave" the single European currency.
"We have taken the decision to be in a currency union. This is not only a monetary decision it is a political one," Merkel said in a BBC interview, speaking in German through a translator.
"It would be catastrophic if we were to say (to) one of those who have decided to be with us, 'We no longer want you.'
"Incidentally the (European Union) treaties don't allow for that anyway. People all over the world would ask, 'Who will be next?' The Euro area would be incredibly weakened."
Asked about the emergence of anti-German sentiment over Berlin's leading role in dealing with the debt crisis, Merkel said: "The European discussion over the euro has become almost domestic politics.
"We debate very harshly in our parliaments and we use tough words. That has characterised Europe-wide debates too."
But she added: "Thankfully we have learnt to solve our conflicts peacefully, to talk about them and to turn this crisis into opportunity."