WASHINGTON, June 17: The US Federal Reserve intervened in the exchange markets to shore up the Japanese yen, the treasury department announced on Wednesday. The United States is "prepared to co-operate in exchange markets as appropriate", a treasury statement said.Press reports in Japan had earlier said that Japanese and US monetary authorities had intervened on the New York foreign exchange market to sell dollars against the yen.The joint action followed the disclosure that Japanese Prime Minister Ryutaro Hashimoto and US President Bill Clinton agreed on Wednesday to co-operate in stabilizing foreign exchange rates. In London, the dollar plunged to 138.75 yen on news of the US intervention.Hashimoto and Clinton made the agreement during telephone talks. Hashimoto is expected to make an announcement shortly. The dollar's surge against the yen triggered falls in Japanese and Asian share prices, which have already been pressured by Asia's financial crisis. In Tokyo, the US dollar was trading at141.98-142.01 yen at 0800 GMT, after falling to low as 144.10 in early trading. The Japanese unit traded at 143.35 in New York late on Tuesday.