U.S. Treasury Under Secretary Lael Brainard on Friday warned the world's biggest economies against taking unilateral steps when it comes to exchange rates.

"All the members of G20 need to deliver on a commitment to move towards a market-determined exchange rate and refrain from competitive devaluation," she said in a speech at a financial conference. "For the adjustment process to work globally, G20 members will have to bring their exchange rate frameworks into alignment so that we grow together and avoid a downward spiral of beggar-thy-neighbor policies,"

Brainard also warned about "loose talk about currencies". When pressed by reporters whether she may have meant Japan, the U.S. officials said that she is not "singling out a particular country."

Christine Lagarde, chief of the International Monetary Fund, dismissed the possibility of an international currency conflict, saying that "the current talk of currency war is overblown."

IMF assessment "does not indicate any major deviation from the fair value of major currencies," she said.

G20 finance ministers and heads of central banks are expected to issue a communique on Saturday, stating their shared view on the global economy. However, several analysts don't expect Japan's recent measures to be singled out in the final statement, with several doubting that exchange rates will be mentioned at all.

Russia's Finance Minister Anton Siluanov, however, expressed hope that the communique would contain a commitment to refrain from competitive devaluation.

Russia used the start of the G-20 meeting to renew its push for a review of the make-up of the IMF and the relative voting strength of its members to reflect growing changes in world economy.

Although the IMF has committed itself to the review, Siluanov said on Friday that he sees "certain difficulties with finding common ground on the road map to solve this issue."

He expressed hope, however, that the financial chiefs will be able to come to a decision at one of the upcoming gatherings of financial ministers before a G20 summit in September.

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