WASHINGTON, US - US Treasury Secretary Timothy Geithner said Thursday he was confident China would allow its tightly controlled currency to be more flexible and reflect market expectations.

Answering questions from an array of lawmakers concerned over the rigid yuan currency, Geithner noted China had made a commitment to allowing the currency to fluctuate.

"China, as I've said many times, has committed to move," he told a congressional hearing. "They understand they need to do it. I think they want to do it. And I'm actually quite confident they will do it."

Geithner said that China and several other Asian nations had intervened in the foreign exchange market, apparently to contain the rise of their currencies.

"The scale of intervention declined dramatically in the peak of the crisis. It started to increase again in China and countries around the world," he said, citing the latest financial crisis which peaked around the end of 2008.

Geithner's remarks came after President Barack Obama, on his maiden China visit, tactfully voiced US worries that China's yuan currency was being kept artificially low to boost Chinese exports.

"I was pleased to note the Chinese commitment, made in past statements, to move toward a more market-oriented exchange rate over time," Obama said as Chinese leader Hu Jintao looked on.

"I emphasized in our discussions, as have others in the region, that doing so based on economic fundamentals would make an essential contribution to the global (economic) rebalancing effort," Obama said.

Hu made no fresh offer of action.

Beijing is under mounting pressure to let the yuan appreciate, with the United States and Europe complaining the currency is being kept artificially low.

A weak yuan has the effect of boosting Chinese exports by making them more competitive overseas.

International Monetary Fund chief Dominique Strauss-Kahn - whose visit to China this week coincided with that of Obama - said Beijing should let the yuan rise "sooner rather than later," saying it would benefit both China and the global economy.

"The renminbi (yuan) is undervalued. It's not only in the interests of the global economy but also in the interests of China to have a revaluation," Strauss-Kahn said.

The yuan's exchange rate with the dollar has been virtually at a fixed rate to the mostly weak US dollar since July 2008, three years after Beijing decided to abandon the Chinese currency's decade-old peg to the greenback.