Fresh worries Tuesday about the health of European banks sent stocks lower in the U.S.

The Dow Jones industrial average fell about 50 points in early morning trading to kick off the start of the holiday-shortened week. Broader markets also fell.

European markets all fell Tuesday after reports said the continent's major banks have more potentially risky government debt on their books than was disclosed during stress tests earlier this year. The banks could be forced to raise more money to protect against potential losses, while also facing more fees from regulators.

The dollar strengthened against the euro and investors bought U.S. Treasurys on the new European bank concerns.

Stocks worldwide dropped during the spring because of worries that mounting government debt in Europe would hurt banks' ability to lend and stunt an economic recovery on the continent. That, in turn, would drag down a global rebound.

Investors could be taking their cues from overseas because there are few domestic economic reports due out this week that could sway traders. A barrage of mostly better-than-anticipated economic data sent stocks sharply higher last week. The reports helped push major indexes to their first winning week in a month.