The 16 eurozone leaders agreed Friday night to set up a defense plan to shield their shared currency against further attack by the time markets open Monday. Their finance ministers will hold an emergency meeting Sunday to work out specifics of the anti-speculation plan.
Merkel said European leaders were going beyond the existing rescue plan for Greece "because we see that the stability of the eurozone as a whole is not yet secured with this Greek program alone."
Merkel offered few details, but said that all eurozone members must "resolutely and acceleratedly" bring down their budget deficits. She also called for stronger financial market regulation.
The eurozone nations will produce "a common instrument to react to speculation or an endangering of the eurozone's stability ... in order to make clear that we as eurozone countries stand by the stability of our currency," she added.
With markets unsettled by the Greek crisis, Spain and Portugal are beginning to show signs of trouble - with borrowing costs increasing, talk of speculative attacks and increasing concern among European partners that some form of help could be required.
Merkel said eurozone leaders took "the right steps" on Friday.
"It is a serious situation," she acknowledged. "If you look at the (bond) spreads from Friday or Thursday, you see that we have a bad development not just in one country but in several countries."
Merkel spoke after meeting Canadian Prime Minister Stephen Harper, whose country currently holds the presidency of the Group of Eight industrial nations.
"Markets bounce up and down and I'm confident that they will see rationality as we move forward," Harper said.
"At the same time, I'm also quite confident that our European friends will take whatever measures are necessary to ensure that the situation moves forward in a positive direction," he added.
Early Saturday, Germany's highest court said it had rejected an attempt to block the country's contribution to the aid package for Greece because such a move could cause serious economic damage.
Parliament on Friday authorized granting as much as euro22.4 billion ($28.6 billion) in credit over three years, and President Horst Koehler signed the legislation into law later in the day.
A group of academics who argue that the package violates the European Union's Lisbon Treaty filed a complaint to the Federal Constitutional Court after the parliamentary vote. They sought an injunction blocking the aid while their case is considered.
The German contribution - which is unpopular at home - is part of a wider euro110 billion package backed by eurozone members and the International Monetary Fund. Germany has Europe's biggest economy.
The court said in a statement it had concluded that issuing an injunction blocking the aid would pose a risk of "serious detriment to the public."