"I think that the heat has to come down a little bit in the conversation," U.S. Treasury Secretary Jack Lew told U.S. broadcaster CNBC in an interview taped Sunday night and broadcast on Monday morning.

Greece's leftist Prime Minister Alexis Tsipras laid out plans on Sunday to dismantle Greece's "cruel" austerity program, ruling out any extension of its international bailout and setting himself on a collision course with his European partners.

Lew, when asked if he was concerned that Greece might leave the euro zone, said Greece needed to work with all its financial partners - which include the "troika" of European Central Bank, International Monetary Fund and European Commission lenders - to reach mutually agreeable terms.

"Everybody's got to tamp down the rhetoric a little bit," Lew said in the Monday broadcast as finance ministers from the Group of 20 gathered in Istanbul.

The Greek situation promises to figure prominently in the meetings. Financial leaders are also expected to discuss the health of the global economy, the recent strength of the U.S. dollar and the ongoing conflict in Ukraine.

Lew said the strong dollar was a good thing because it reflected a turnaround of America's economy. He said we would have conversations with European counterparts in the coming days about diplomatic efforts to end the war in Ukraine, support for Kiev and sanctions against Russia for its role in the conflict.