"We've been engaged with the Chinese now for over two years in discussions on the direction of their currency," Snow told CNBC television on Monday.

"They've committed to move to greater flexibility. They've taken a lot of steps to accommodate greater flexibility through improvements in their financial system. We think they're ready and we think now is the time for them to move."

A top Chinese finance official said recently that Beijing has no timeframe for reform of its foreign exchange system, despite increasing pressure from the United States and others to throw open its currency regime.

Washington argues a currency modification may help ease the trade deficit and other economic imbalances.

"We have talked extensively about the move to greater flexibility and they know our position," Snow said.

"We're disappointed they haven't moved, we are not happy with where they are and now is the time for them to move."