The yen slipped on Tuesday but held on to most of its intervention-driven gains, after last week's joint action by Tokyo and Washington to shore up the currency kept speculators wary of rebuilding bearish positions. The yen was last down 0.4% at 157.8 per dollar, giving back some of its gains after hitting a three-month high of 155.20 in the previous session, but remaining well above its 40-year low of 163.99 touched in July. The Japanese currency had surged as much as 5% over the last three trading sessions, with Japan confirming coordinated yen-buying intervention on Friday with the U.S. in a rare move. Two market sources told Reuters the U.S. Treasury bought yen for euros last week instead of selling dollars, a highly unusual move likely aimed at helping Japan strengthen the yen without encouraging a view that Washington wants a softer dollar. Against the euro, the yen slipped 0.5% to 181.62, down from Monday's almost nine-month high of 179.44.