The yen slumped near a four-year low against the dollar and a three-year trough against the euro on Monday after the Bank of Japan kicked off its aggressive monetary easing program in an attempt to beat persistent deflation. The Japanese currency looked poised to extend its weakness, pushing the dollar above the significant 100 yen level as early as this week, analysts said. That would mark the weakest since April 2009 for the yen.
The dollar rose as high as 99.04 yen on Reuters data, the strongest level since May 2009, before pulling back slightly to trade at 98.96 yen, up 1.5 percent on the day. The euro climbed 1.5 percent to 128.63 yen, having risen as high as 128.83 yen, its highest since January 2010. Against the dollar, the euro gained 0.1 percent to $1.2999, shrugging off concerns about Portugal's ability to keep its bailout program on track after a constitutional court rejected some of the government's austerity measures.