Just eight months ago, Brazilian Finance Minister Guido Mantegadeclared a “truce” in competitive currency devaluations. Now,Japanese and Swiss moves to weaken the yen and the franc showreviving tension in foreign-exchange markets as the deterioratingU.S. economy weighs on the dollar.

Japan sold yen today, causing the currency to weaken as much as4 percent against the dollar after rising 5 percent last month.“Ongoing one-sided moves” would hurt the recovery from a Marchearthquake, Finance Minister Yoshihiko Noda said. Yesterday, theSwiss National Bank cut interest rates to rein in the franc after again of about 36 percent in the past 12 months.

Europe's sovereign debt crisis and the battle between Republicanleaders and U.S. President Barack Obama over the budget andborrowing limits drove investors to the perceived safety of yen andfrancs. The risk of a U.S. return to recession, forcing the FederalReserve to another round of monetary easing, has exacerbated dollarweakness. The currency's drop last year left all of Asia's 10biggest economies seeking to influence their own exchange rates toaid exporters and growth.