The euro weakened for a third day against the dollar, touching the lowest in almost three weeks, as concern the currency region's rescue plan will crumble and the European Central Bank will cut interest rates damped demand.

The 17-nation currency fell the most in two weeks versus the yen after Greek Prime Minister George Papandreou pledged to put the European Union's latest accord to a referendum, risking pushing the country into default if rejected by voters. The dollar and yen strengthened as stocks slid around the world and a Chinese report showed manufacturing slowed. Australia's dollar declined after the nation's central bank cut interest rates.

"There are continued political problems surrounding the implementation of the recent austerity measures in Greece," said Michael Woolfolk, senior currency strategist in New York at Bank of New York Mellon Corp., the world's largest custodial bank. "In this environment, there's always going to be negative developments, and we're focusing on them right now, which is benefiting the U.S. dollar."