The yen is again approaching a three-decade low against the dollar Monday, drawing a verbal warning by a Tokyo currency official. Less than two months after Japan spent more than $60 billion to prop up the yen, the currency's gains have disappeared, as traders revert to the view that the interest-rate gap will stay wide between the U.S. and Japan. Late Monday in Tokyo, the yen was trading at around 159.70 to the dollar, close to the level in late April that triggered currency intervention.