Japan and the United States will "certainly" conduct joint intervention again if the yen shows signs of resuming its downtrend, said Atsushi Takeuchi, a former central bank official involved in Tokyo's market forays more than a decade ago. The yen held gains above recent 40-year lows on Monday after the two countries launched a rare joint yen-buying intervention in a show of determination to combat a sell-off in the currency. Takeuchi said the latest joint action was highly effective in creating market perceptions that one-way weakening of the yen will not continue.