July 13 (Bloomberg) -- Iran asked Japanese refiners to switch to the yen to pay for all crude oil purchases, after Iran's central bank said it's cutting holdings of the U.S. dollar.

Iran wants yen-based transactions ``for any/all of your forthcoming Iranian crude oil liftings,'' according to a letter sent to Japanese refiners that was signed by Ali A. Arshi, general manager of crude oil marketing and exports in Tehran at the National Iranian Oil Co. The request is for all shipments ``effective immediately,'' according to the letter, dated July 10 and obtained by Bloomberg News.

The yen rose on expectations for an increase in demand for the currency to buy shipments from Iran, Japan's third-largest oil supplier. Central bankers in Venezuela, Indonesia and the United Arab Emirates have said they will invest less of their reserves in dollar assets because of the weakening currency, while the United Nations Security Council is preparing for another round of sanctions against Iran because of the nation's nuclear research.

``What else can Japan do but to accept the request, once the oil producer sent its wish?'' said Hirofumi Kawachi, an analyst at Mizuho Investors Securities Co. in Tokyo. ``The tensions between the U.S. and Iran are escalating, and it's Iran's measure to hedge risk.''

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