Yellen mum on yen intervention

US Treasury Secretary Janet Yellen acknowledged sharp moves in the value of the yen last week, even as she declined to say whether Japan had intervened to support the currency.

"I'm not going to comment on whether they did or didn't intervene," Yellen said. "I think that's a rumor."

Still, she said the yen "did move quite a bit in a relatively short period of time," adding, "we would expect these interventions to be rare and consultation to take place."

Japanese authorities appeared to enter the market to support the yen on two occasions in the past week. One came after the yen weakened beyond 160 to the US dollar for the first time in 34 years, followed by another after US Federal Reserve Chair Jerome Powell said a hike was unlikely to be the US central bank's next interest-rate move.

It came after former US Treasury Secretary Lawrence Summers said that currency interventions are ineffective at shifting exchange rates, even at the large magnitude that Japan has been thought to have deployed recently as it will be overwhelmed by the broad magnitude of private sector capital flows.