WASHINGTON (MarketWatch) — Treasury Secretary Timothy Geithner on Wednesday stepped up the pressure on China, effectively blaming the world’s number-two economy for the emergence of what some are calling a “currency war” ahead of an important global gathering.

The U.S. believes that it is important to see more progress by major emerging economies to move to more flexible, market-oriented exchange rate systems, Geithner said in advance of an annual International Monetary Fund gathering in Washington set for later this week.

U.S. Treasury Secretary Tim Geithner smiles as he speaks on U.S. economic policy at the Brookings Institution. Reuters

“It is unfair to countries that were already running more flexible regimes and let their currencies appreciate,” Geithner said, focusing a large part of his comments at a Brookings Institution event on China’s exchange rate policy. See MarketWatch's full coverage of the IMF meeting.

“And it requires a cooperative approach to solve, because emerging economies individually will be less likely to move, unless they are confident other countries would move with them.”

While China said in June that it would allow more exchange-rate flexibility, there has been little movement since then in the yuan/dollar rate USDCNY, -0.00% .

Geithner argued that when large economies with undervalued exchange rates act to keep the currency from appreciating, that encourages other countries to do the same, setting off a “dangerous dynamic.”

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The Geithner comments came as the head of the International Monetary Fund, Dominique Strauss-Kahn, warned in an interview against countries using currencies as “policy weapons.”

In comments to the Financial Times, Strauss-Kahn said: “Translated into action, such an idea would represent a very serious risk to the global recovery...Any such approach would have a negative and very damaging longer-run impact.”

Continuing to talk about the relationship between China and the U.S., Geithner also argued that with America saving more, emerging countries that are overly reliant on exports to the U.S. -- such as China -- must change their policies or else global growth will slow.

Geithner said countries that run “chronically” large surpluses need to change their policies to boost their domestic demand.

Geithner’s comments and the IMF meeting come after the House of Representatives ramped up pressure on China on Sept. 29 to boost the value of its currency, with U.S. lawmakers approving legislation that could lead to duties on Chinese exports considered unfairly cheap because of undervalued currency. Read about the China currency bill