The U.S. dollar and euro rallied 1.5 percent versus the yen on Friday after Japan said the Group of 20 countries did not oppose its aggressive monetary easing aimed at beating deflation rather than at weakening its currency.
Traders said hedge funds resumed buying the dollar against the yen, leaving the pair poised to test strong resistance and option barriers at the 100 yen level in the coming days. The dollar hit a four-year high of 99.94 yen last week.
Japan's Finance Minister Taro Aso said: "Japan explained that its monetary policy is aimed at achieving price stability and economic recovery, and therefore is in line with the G-20 agreement in February."
(Read More: Any G-20 Criticism Unlikely to Derail Yen's Fall)
Newly installed Bank of Japan Gov. Haruhiko Kuroda said the monetary policy stance gained broad understanding, but some emerging market nations said Tokyo must be mindful of the negative impact its flood of cash can have on investment flows into their higher-growth economies.
Earlier this week, a senior International Monetary Fund official said Japan's easing via a $1.4 trillion BOJ monetary stimulus plan is a welcome step in reviving the economy.
Outgoing Bank of Canada Gov. Mark Carney said Japan's action is consistent with the G-20 communique that called for countries to refrain from competitive devaluation. Carney, the head of the G-20's Financial Stability Board, takes over the Bank of England in July.
(Read More: What the G-20 Need to Talk About This Week)
"It appears with Kuroda's and Aso's comments and the G20's acceptance of their explanation on monetary policy that the path is clear for the BOJ to both continue easing or enact additional easing measures if needed. This is leading to the late day sell-off in the yen," said Brian Daingerfield, currency strategist, at RBS Securities in Stamford, Conn.
A lockdown and city-wide search for a suspect in the Boston Marathon bombing after another suspect was killed may have contributed to reduced trading volume, analysts and traders said. The lack of economic data releases on Friday and the ongoing meetings of global policymakers in Washington also hurt volume.
Brad Bechtel, managing director at foreign exchange brokerage Faros Trading in Stamford, said his firm saw less liquidity than normal for a Friday morning.
"We have a big asset manager account in Boston and they are generally big players in the FX space. But today they're unable to do their jobs. That is keeping liquidity down," he said. "A lot of folks in Boston are out of the market and anyone not in Boston is stuck watching the TV trying to find out what's going on there."
School holidays in Boston could also be contributing to lower activity from Boston-based accounts, asset managers said.
The dollar was last up 1.4 percent to 99.50 yen, having hit a one-week peak of 99.68 yen, according to Reuters data.
"Many might have expected the G-20 to bring up criticism of the BOJ for running monetary stimulus. This has not been the case. Market participants see that as a green light for the yen to go lower," said Tatjana Michel, currency strategist at Charles Schwab in San Francisco.
"We definitely see the yen lower in the next couple of months due to this massive stimulus. I see the dollar going to 110 yen by the end of the year," she said.
The euro last traded up 1.4 percent to 129.90 yen. It reached a session peak of 130.24 yen and looked on course to test last week's three-year high of 131.11 yen.
The euro gave up most of its early gains against the dollar, trading just above break-even on the day at $1.3057, having risen to a session high of $1.3128 after European Central Bank board member Jens Weidmann said interest rates in Europe are appropriate.
But if data shows change, the ECB needs to reassess rates, he said.
The euro lost 1.1 percent on Wednesday, its worst daily performance since June, after Weidmann was quoted by the Wall Street Journal saying the bank could ease further if economic data warrants it.
"Weidmann clarified that comments in the WSJ were not meant to signal a trend change on ECB rates," said analysts at Action Economics.
Earlier, the euro also got a brief boost after German Finance Minister Wolfgang Schaeuble said the ECB should try to limit the amount of liquidity in the euro zone, although he also acknowledged the "precarious" economic plight of some countries in the region.