President Obama has welcomed the announcement by the Chinese central bank that it's to gradually allow the exchange rate of its currency, the yuan, to become more flexible. Mr Obama called it a constructive step. But the Chinese central bank has ruled out any single large-scale revaluation of the yuan, and one leading Democrat described the move as vague and limited. More now from our correspondent David Willis in Washington.

China pegged the yuan to the US dollar nearly two years ago in order to make Chinese goods more affordable and help its manufacturers compete in the global market. But the move has been a source of friction between China and many of its trading partners, in particular the United States who contended limiting the value of the yuan was giving Chinese exporters an unfair advantage and costing millions of American jobs.