A key gauge of the dollar's strength hit its highest level in four months on Monday as many of the greenback's rivals weakened. The ICE U.S. Dollar Index, a popular gauge of the buck's value against a basket of rivals,

The euro fell to a four-and-a-half-month low against the dollar and might struggle to recover as interest rate differentials move against the exchange rate, ING said, adding that only position adjustments will likely generate any euro strength this week and any gains would be limited.

The euro dropped to its lowest level in 6-1/2 months against the greenback on Monday as investors worried about possible U.S. tariffs that would hurt the euro area's economy. Meanwhile, the U.S. dollar index -- a measure of its value relative to a basket of foreign currencies -- slightly overshot the highs seen right after the U.