NEW YORK (CNN/Money) - U.S. stocks tumbled early Monday, extending the previous week's declines, on jitters about national security issues in response to potential al Qaeda links to last week's deadly bombings in Madrid, as well as Spain's surprise change of government.

After ten minutes of trading, the Dow Jones industrial average (down 36.08 to 10204.00, Charts), the Standard & Poor's 500 (down 4.59 to 1115.98, Charts) index and the Nasdaq composite (down 11.10 to 1973.63, Charts) all declined, most notably the Nasdaq.

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After seven weeks of flat to lower trade, the major indexes tumbled last week in a steep multi-session selloff. A rally on Friday was not enough to wipe out the previous four sessions' declines. Investors cashed out of a variety of issues on concerns that valuations have gotten too high, while the economic recovery is hitting roadblocks, at least as far as the labor market is concerned.

Analysts said that this period of consolidation -- following the 2003 and early 2004 rally -- is likely not over yet. This seemed to be confirmed in the early trading Monday.

The latest developments surrounding last week's terrorist attack on the Madrid rail system that left 200 dead and hundreds more injured weighed on stocks. News that one of the suspects in the attack may have al Qaeda links shook up investors. The surprise win of the Socialist Party in Sunday's elections in Spain also proved unsettling, particular as the Prime Minister elect vowed to pull Spanish troops out of Iraq in the next few months.

In addition, of late, the economic news has been less robust than expected. Released before the bell Monday, the New York Empire State index, a gauge of manufacturing in the state, fell to 25.3 in March from 42 in February. Economists surveyed by Briefing.com expected the index to fall to 38.9.

In a separate report, the Federal Reserve said that production at the nation's factories, mines and utilities rose in February, more than expected, while capacity utilization ticked up as well.

Treasury prices gained, pushing the 10-year note yield down to 3.76 percent from 3.77 percent late Friday. The dollar edged lower versus the euro and yen.

Among commodities markets, Brent crude oil futures gained 17 cents to $31.86 a barrel in London. COMEX gold rose $4 to $399.60 an ounce.

European markets fell at midday there, while Asian markets closed with gains Monday.