She added that the swaps contracts - complex securities that played a central role in the financial crisis after the collapse of Lehman Bros. Holdings in 2008 - were not regulated, but "must be made transparent" amid efforts to tighten financial regulation.
A full-scale debt restructuring in Greece also could prove contagious, leading investors to question the stability of other European nations that otherwise would not need assistance from the European Union to meet their financing needs, she said.
Merkel wants to get private creditors to volunteer to contribute to the next aid package for Greece, an initiative for which she does not yet have a majority among the leaders of the 27 EU nations holding a summit Thursday and Friday in Brussels, Belgium.
However, Merkel voiced confidence that other EU leaders would follow Germany, France, and the Netherlands in supporting the privatization idea.
How much money private creditors might contribute remained unclear, but Merkel insisted it must be "substantial . . . and measurable."
The EU summit comes after Greek Prime Minister George Papandreou survived a vote of no-confidence early Wednesday, paving the way for an even tougher vote next week on a new package of austerity measures.
Adopting the spending cuts and tax hikes "is the required precondition to discuss the question of a new program," Merkel said.
Last year's $159 billion loan package by the EU, the European Central Bank, and the International Monetary Fund was based on expectations that Greece could return to bond markets, but borrowing costs remain prohibitive, requiring a new bailout to meet the nation's financing needs.
The new program - likely to figure high on the EU summit's agenda - is expected to be similar to last year's in its amount and is meant to secure Greece's financing needs through 2014.