"China is committed to promoting the reform of the renminbi (yuan) exchange rate regime," foreign ministry spokesman Hong Lei told reporters.

"A great many facts prove that the renminbi exchange rate is not the main cause for the trade imbalance between China and the United States."

Hong was referring to a bill by three US senators to seek to penalize China for alleged currency "manipulation" that has kept the yuan artificially undervalued and helped boost already swollen Chinese exports to the United States.

The bill announced Monday came on the eve of a state visit to the United States by President Hu Jintao.

"Our message to President Hu is, 'Welcome to America, but we want to make sure we have a fair trading system,'" said Michigan Senator Debbie Stabenow, who joined fellow Democrats Charles Schumer and Bob Casey in the announcement.

The bill to be introduced in the new Congress would "vigorously address currency misalignments that unfairly and negatively impact US trade," the three said in a joint statement.

In the past, similar efforts have had little impact on Beijing, despite claims from Washington and other trading partners that the Chinese yuan is undervalued by as much as 40 percent to help boost exports.

Hong similarly dismissed the pending bill as an attempt to harm US-China relations.

"We hope the relevant US lawmakers can... promote the stable healthy development of China-US economic and trade relations and avoid harming China-US economic and trade cooperation," Hong said.