Greece's prime minister lashed out Monday at Germany—its chief euro-zone benefactor—for tough talk on government-debt defaults, making clear the widening strains inside the 16-member euro-zone as the currency bloc wrestles with a teeming sovereign-debt crisis.

Addressing reporters in Paris, George Papandreou said the Germans' view—long-held, but recently reiterated—that private bondholders could suffer losses as part of a future bailout was intensifying government-debt woes.

The...