By Glenn Somerville

WASHINGTON | Fri Dec 17, 2010 11:01am GMT

WASHINGTON (Reuters) - The head of the International Monetary Fund said on Thursday he was worried that EU leaders' piecemeal approach to Europe's debt crisis was encouraging markets to pick off weak countries one by one.

Dominique Strauss-Kahn appeared to endorse the idea of common euro bonds, saying they could be a useful tool, but added the political will to give power to the center of Europe was the main hurdle to their creation.

"I am worried, and that's why I am urging the Europeans ... to provide a comprehensive solution because this piecemeal approach ... obviously doesn't work," Strauss-Kahn told Reuters. "The markets are just waiting for what's next."

Due to its cumbersome decision-making structure, the euro zone has tended to offer countries such as Greece and Ireland rescues only once they were "at the edge of the cliff," he said. That approach has created a domino effect.