NEW YORK (Bloomberg) — The dollar rose to a six-month high against the euro and increased the most in three weeks versus the yen as US gross domestic product exceeded forecasts, growing at the fastest pace since 2003.

The euro headed for its biggest monthly drop against the yen in a year on concern Greece's budget problems will spread. The franc fell from a 10-month high against the euro on speculation Switzerland's central bank intervened in currency markets to curb its strength and support the nation's economy.

"The dollar was strong already, and it's continued the trend," said John Norris, senior market strategist at Brewer Investment Group in Chicago. "Any time the numbers beat expectations that significantly, it's good news."

The US currency advanced 0.7 percent to $1.3879 per euro Friday in New York. It reached $1.3863, the strongest level since July 9. The dollar increased 0.5 percent to 90.39 yen. It earlier advanced 1.1 percent, the biggest intraday gain since January 7. The yen advanced 0.1 percent to 125.45 per euro, from 125.63, after earlier touching 124.82, the strongest level since April 28.

The euro may fall below $1.35 if it sustains a drop past $1.38, the 50 percent Fibonacci retracement of the rally from its March 4 low of $1.2457, said Richard Ross, a global technical strategist at Auerbach Grayson Co. in New York. The 16-nation currency may reach $1.3483, the next Fibonacci level, according to Ross.

"The euro is on a pretty precipitous slope," Ross said. "This isn't a correction any more. It's looking more like a cyclical bear market."

Fibonacci analysis is based on the theory that securities tend to rise or fall by specific percentages after reaching a new high or low. A break through one level indicates a currency may move to the next line. A failure to break through indicates a trend may be ending.

The franc weakened as much as 0.4 percent to 1.4765 after appreciating to 1.4636, the strongest level since March 10, two days before the central bank intervened. Central banks intervene by buying or selling currencies to influence exchange rates.

Swiss National Bank President Philipp Hildebrand, in Davos, Switzerland, for the annual meeting of the World Economic Forum, declined to comment. No one at the Bank for International Settlements was immediately available for comment.

"We could associate this possibly with action from the Swiss National Bank," said Russ Oxley, head of rates in Glasgow at Ignis Asset Management, which has £71 billion ($114 billion) of assets. "People thought they were much more comfortable with the strength of the euro, but that obviously seems to have been a false impression."

The dollar strengthened as the Commerce Department reported that gross domestic product increased at a 5.7 percent annual pace from October through December, the fastest in six years. The median forecast of 84 economists in a Bloomberg News survey was for a 4.7 percent advance.

"With good news, the market reacted in favour of the currency," said Ronald Leven, currency strategist at Morgan Stanley in New York. "The dollar will hold up pretty well."

The euro has fallen 5.1 percent versus the yen in January, its biggest monthly drop since depreciating 9.1 percent in January 2009.