U.S. Treasury Secretary Jack Lew said on Wednesday he was worried that a miscalculation could lead to a new Greek crisis, which would be a mistake to think would have no consequence for the wider world.

"The challenge for the Europeans, the political and economic institutions — the IMF — is to show enough flexibility," Lew said at the London School of Economics.

"So if the Greeks are prepared to take the kinds of tough steps that they need to take, they find a pathway to resolving this without there being an unnecessary crisis."

Lew also said that conversations between central bankers in the United States have shown they have increasingly understood the need to be clear in their communications.

"The converations amongst central bankers have shown an increasing understanding in the need to be clear in communication, and I think I'll leave it with them to communicate those messages," said Lew after being asked about the prospect of a U.S. Federal Reserve rate hike.

Speaking at the London School of Economics, Lew also described an early-year slump for the U.S. economy as "somewhat anomalous" and added that the labor market was showing signs of continued recovery and growth.