The bill, sponsored by Republican Senator Lindsey Graham and Democratic Senator Charles Schumer, would impose 27.5 percent tariffs on Chinese imports if the currency dispute is not settled. The lawmakers said if the pace of China's currency reform slowed, they would call for a vote.

The media reported little about the currency topic during a visit by U.S. Commerce Secretary Carlos Gutierrez to Beijing on the heels of the two senators.

Chinese Vice Premier Wu Yi will leave Beijing on Monday for Washington to co-chair the 17th meeting of the Sino-U.S. Joint Commission on Commerce and Trade with Gutierrez and U.S. Trade Representative Rob Portman. The two sides will discuss their respective concerns, China's Foreign Ministry has said.

China's foreign currency reserves are boosted as the country buys dollars and other foreign currencies that come into the economy, amid booming foreign trade, and stockpiles them in U.S. Treasury bonds and other assets -- as a means of foreign exchange controls and to guard against possible inflation, analysts say.

The China Business News has reported, citing unnamed sources, the nation's foreign currency reserves reached 853.7 billion U.S. dollars by the end of February, likely topping Japan's to become the world's largest. Government figures were only released on a quarterly basis.

Central banker Zhou Xiaochuan, however, has said it is "not reliable" to achieve Sino-U.S. trade balance only through adjusting exchange rates.

Li Chao, a spokesman for the People's Bank of China (PBoC), or the country's central bank, also contended last week that the skewed trade with the United States was an outcome of a high savings rate in China as against an extremely low one in the United States. In theory, excess savings produce trade surpluses, and vice-versa, savings shortfall means deficits, he acknowledged.

China will not have another one-off revaluation of yuan, he said, echoing an earlier claim by Premier Wen Jiabao.

The PBoC early this year began a new policy of calculating the yuan's benchmark value against the U.S. dollar using a weighted average of the prices given by major banks. The highest and lowest offers are excluded from the calculation.

Giving banks a role in setting the daily exchange rate is seen as a sign that the central bank is willing to allow market forces a greater role in daily trading, analysts acknowledge.

But the yuan is allowed to move 0.3 percent up or down from the benchmark value against the dollar per day. "Only propelled by new market factors can the floating band be enlarged," said director Xia Bin with the finance research institute of the State Council Development Research Center.