Wall Street opens lower after Brussels explosions

European markets fell, while gold and government bonds firmed up, airline and travel-related stocks were the worst hit

Wall Street opened lower on Tuesday after explosions in Brussels sparked fresh geopolitical concerns and sent investors scurrying for safe-haven assets.

At least 34 people were killed in twin attacks on Brussels airport and a rush-hour metro train in the Belgian capital, triggering security alerts across western Europe.

European markets fell, while traditional safe havens gold and government bonds firmed up as reports of the events in the de facto capital of the European Union unfolded. Airline and travel-related stocks were the worst hit.

Shares of American Airlines, Southwest Airlines and Delta Airlines, were down between 3% and 1.6%. The broader NYSE Arca Airline index was down 1.8%. Gold rose 1% to $1,255 an ounce, while oil prices were swept lower.

"With economic growth so tepid around the world, including in the United States, the susceptibility to any type of terrorist attacks could highlight the market's fragility," said James Abate, chief investment office of Centre Funds in New York.

Markets have reacted negatively to terrorist attacks such as the one in Paris last November, before quickly recovering.

At 9:39 am ET (1339 GMT), the Dow Jones industrial average was down 57.32 points, or 0.33%, at 17,566.55, the S&P 500 was down 8.23 points, or 0.4%, at 2,043.37 and the Nasdaq Composite was down 13.65 points, or 0.28%, at 4,795.22.

Goldman Sachs was the biggest drag on the Dow, while Apple's 0.4% drop weighed the most on the S&P 500 and the Nasdaq.

All 10 major S&P sectors were lower, with the financial index's 0.70% loss leading the decliners.

Cruise operator Carnival Corp's shares were down 2.2% at $48.66, while travel-website operator Expedia was off 1.9% at $108.79 and peer Priceline fell 2.2% to $1321.49.

For financial markets, the events in Brussels come at a time when liquidity is starting to dry up ahead of the Easter holiday and investors are planning to cash in on a steep rally in stocks over the last few weeks.

The S&P 500 has risen about 8% in the past five weeks and is about 4% away from its all-time high.

"We're getting to the point in time where we're overbought in the short run. I wouldn't be surprised heading to the long weekend if we saw some profit taking," said Art Hogan, chief market strategist at Wunderlich Securities in New York.

The Brussels attacks eclipsed encouraging economic data out of the euro zone, while Asian shares had faltered earlier over hints from US Federal Reserve policymakers about an earlier-than-expected increase in interest rates.

Declining issues outnumbered advancing ones on the NYSE by 2,041 to 593. On the Nasdaq, 1,436 issues fell and 769 advanced.

The S&P 500 index showed one new 52-week high and no new lows, while the Nasdaq recorded seven new highs and five new lows.