Treasury Secretary Timothy Geithner said on Thursday that key emerging-market nations must let their currencies rise in value in order permit more stable global growth.

In an interview in Tokyo with Japanese broadcaster NHK, Geithner appeared to refer to China when he spoke about the role of emerging market countries in creating a more stable monetary system.

You want to see those currencies continue to reflect the substantial upward pressure you're seeing in fundamental economic forces that are going to push them gradually to appreciate and strengthen against the dollar, the yen and the euro, he said.

It's going to have to continue on a sustained basis.

Geithner was wrapping up a quick visit to Beijing and Tokyo that was principally aimed at soliciting cooperation in tightening sanctions against Iran to curb its disputed nuclear program.

Geithner was asked whether the International Monetary Fund should play a larger role in helping the Euro zone countries deal with their debt crisis. He said the IMF was already helping and Europe needs to get a grip on its own problems.

We have a very good record of moving very, very quickly to make it possible for the IMF to do what it needs to do to help its member states but we have to make sure that Europe moves first and gives the world something that the world can support, Geithner said.

(Reporting By Glenn Somerville; Editing by Andrew Hay)

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