U.S. stocks were lower on Thursday after weaker-than-expected retail sales and as the European Central Bank failed to offer additional measures to stop a debt crisis from engulfing the euro zone.

U.S. April same store sales rose 0.5 percent versus the estimate of a 1.7 percent increase, according to Thomson Reuters, sparking concerns about the health of consumer spending.

U.S. retailers, including discounter Costco Wholesale Corp and Target Corp , posted slightly disappointing April same-store sales.

Shares of Costco fell 3 percent to $58.61, while Target dropped 1 percent to $55.48. Wal-Mart Stores Inc dipped 0.9 percent to $54.27.

Tim Ghriskey, chief investment officer of Solaris Asset Management in Bedford Hills, New York, said the consumer is holding back.

While economic data on the consumer has improved, and, anecdotally, we see a lot of people in stores, it doesn't look like in April there was much (spending), he said. It calls into question the strength of consumer and willingness to step up and spend.

The Dow Jones industrial average <.DJI> was down 31.44 points, or 0.29 percent, at 10,836.68. The Standard & Poor's 500 Index <.SPX> was down 3.84 points, or 0.33 percent, at 1,162.06. The Nasdaq Composite Index <.IXIC> was down 7.18 points, or 0.30 percent, at 2,395.11.

The European Central Bank left monetary policy unchanged, but investors were disappointed the ECB did not discuss the outright purchases of European sovereign debt. ECB President Jean-Claude Trichet dismissed out of hand the prospect of a Greece debt default.

Peter Cardillo, chief market economist at Avalon Partners in New York said the decision to keep the monetary policy unchanged was expected, but with the euro collapsing, investors who wanted to see some sort of a defensive movement by the ECB.

(Reporting by Angela Moon; editing by Jeffrey Benkoe)