The yen weakened beyond 99 per dollar for the first time since May 2009 on speculation Bank of Japan measures to fight deflation announced last week will further debase the currency.

The yen dropped against all its 16 major counterparts for a third day after BOJ officials said last week they will boost monthly bond purchases to 7.5 trillion yen ($80 billion), exceeding the 5.2 trillion yen forecast by economists surveyed by Bloomberg News. The dollar declined for a fourth day versus the euro before Federal Reserve Chairman Ben S. Bernanke speaks today. South Korea's won slid to an eight-month low as military tensions on the Korean peninsula escalated.

"It's more of the same right now and the conversation has diverged into where's the money going to end up," Geoffrey Yu, a senior currency strategist at UBS AG in London, said in a phone interview of yen depreciation. "The yen flows, at the end of the day, they're driven by yield."