The euro weakened for an eighth day against the dollar as Greek politicians struggled to form a new government, fueling concern the nation will leave Europe's currency union.

The 17-nation currency extended its run of losses to the longest since September 2008 as Spain's 10-year bond yields climbed back above 6 percent. The pound fell for a second day against the dollar as a report showed U.K. retail sales fell the most in more than a year. The dollar and yen rose against most of their major counterparts on increased demand for haven assets. Canada's dollar dropped to a three-month low as oil declined for a sixth day.

“It's a function of the uncertainty in Greece and the credit stress in Spain,” said Boris Schlossberg, director of research at online currency trader GFT Forex in New York. “It appears to be absolutely clear that the Greeks are not going to do any more austerity. If the Spanish yield goes to 7 percent, it's going to be getting into the red zone — a warning zone for the euro.”