* Futures down: Dow 46 pts, S&P 7.25 pts, Nasdaq 18 pts
By Abhiram Nandakumar
March 22 (Reuters) - U.S. stock index futures were lower on Tuesday after explosions in Brussels sparked fresh geopolitical concerns and sent investors scurrying for safety.
* Two explosions tore through Brussels airport on Tuesday morning, killing 13 people in what Belgian public broadcaster VRT called a suicide attack, and another blast struck a metro station in the capital shortly afterwards.
* Global markets tanked, while crude prices and 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.
* "Anything like the events we're seeing in Brussels this morning is going to weigh on risk sentiment and risk appetite," said Michael Hewson, chief market strategist at CMC Markets in London.
* Shares of cruise operator Carnival Corp were down 3.7 percent at $47.93 premarket, while travel-website operator Expedia was off 1.7 percent at $109 and peer Priceline fell 1 percent to $1336.60.
* Southwest Airlines fell 1.6 percent to $44.25 and American Airlines was off 1.1 percent at $43.
* The attacks eclipsed encouraging economic data out of the euro zone, while Asian shares had faltered earlier over comments from U.S. Federal Reserve policymakers hinting at an earlier-than-expected increase in interest rates.
* Wall Street ended little changed on Monday as investors turned cautious after a five-week rally.
* Wynn Resorts was up 1.2 percent at $93.88 after Morgan Stanley upgraded the stock to "overweight."
Futures snapshot at 6:38 a.m. ET:
* Dow e-minis were down 46 points, or 0.26 percent, with 28,896 contracts changing hands.
* S&P 500 e-minis were down 7.25 points, or 0.35 percent, with 184,049 contracts traded.
* Nasdaq 100 e-minis were down 18 points, or 0.41 percent, on volume of 23,391 contracts. (Reporting by Abhiram Nandakumar in Bengaluru, additional reporting by Jamie McGeever in London; Editing by Don Sebastian)