U.S. Treasury Secretary takes a swipe at Chinese G20 hosts

He also used his speech to call for a stronger International Monetary Fund and to defend U.S. policies, acknowledging that past failures had caused much damage but saying the government was aiming to stabilise debt levels to avoid future problems.

The G20 seminar was spear-headed by France, which is pushing a bold reform agenda in its year-long presidency of the group, and was meant to be focused on ills in the monetary system.

Geithner offered a straightforward diagnosis.

While major currencies moved freely and most emerging economies were well along that path, there were still some with little exchange rate flexibility and extensive capital controls, he said.

This asymmetry fuelled inflation risks in the economies whose exchange rates are undervalued, magnified currency appreciation in others and also generated protectionist pressures, he added.

"This is the most important problem to solve in the international monetary system today. But it is not a complicated problem to solve," he said, according to the prepared text of his remarks.

"It does not require a new treaty, or a new institution. It can be achieved by national actions," he added.

Although Geithner did not mention China by name, the United States has long called on Beijing to let its currency rise more quickly, accusing it of keeping its exchange rate artificially cheap to give its exporters an unfair advantage.

In recent months, Geithner has taken to casting the Chinese currency as a broader global problem, saying that it is making life difficult for other developing economies. India and Brazil, among others, have agreed, saying that a cheap yuan has undermined their competitiveness.

The Chinese government told countries attending the G20 seminar in the eastern city of Nanjing not to mention specific currencies in their speeches and to keep their focus on broader questions in the global monetary system, according to a source attending the meeting.