US FEDERAL Reserve chief Ben Bernanke has hit back at critics of US monetary policy, saying it had calmed markets and was already promoting "moderate but meaningful" growth.

Speaking in Frankfurt, Mr Bernanke had harsh words for China's currency strategy and suggested that a "two-speed global recovery" was more of a risk than the decision to pump $600 billion into the US economy.

"Financial conditions eased notably in anticipation of the [ Fed] committee's announcement, suggesting that this policy will be effective in promoting recovery," Mr Bernanke said.

"The dollar's role as a safe haven during periods of market stress stems in no small part from the underlying strength and stability that the US economy has exhibited over the years."

Among those listening to Mr Bernanke were German finance minister Wolfgang Schäuble, who has dismissed as "hopeless" the US quantitative easing effort.

After much scepticism from Europe on the QE2 measures, ECB president Jean-Claude Trichet sounded a consensual note.

He told his visiting US colleague: "You know to which extent we strongly share the view a strong dollar vis-a-vis the other major floating currencies is very important and the view that you have expressed . . . vis-a-vis surplus countries with exchange rates that are insufficiently flexible."

Mr Bernanke reiterated the US insistence that China was keeping the value of its currency artificially low. "Why have officials in many emerging markets leaned against appreciation of their currencies toward levels more consistent with market fundamentals?" he asked.

Anyone motivated by boosting exports, he said, overlooked "important drawbacks, both for the world system and for the countries using that strategy.

"The emerging market versus emergency market dichotomy is one that I think requires a lot more attention," Mr Bernanke said in a panel discussion.