Stocks index futures fell on Tuesday in the wake of a disappointing revenue miss from Alcoa and Japan's upgrade of the severity of its nuclear crisis.

Investors were cautious after Japan raised the severity of the Fukushima nuclear power plant accident to the highest level on the International Nuclear and Radiological Event Scale, putting it on par with the Chernobyl 1986 disaster.

Earnings news will be another focus after Alcoa Inc reported revenue that missed forecasts after the bell on Monday, which sent the company's shares lower in post-market trade despite its reporting a first-quarter profit above expectations.

Mining stocks will also be in focus as metals prices fell on worries Japan's massive earthquake and a nuclear crisis would weaken recovery prospects in the world's third-largest economy.

Selling in key commodities were also triggered after Goldman Sachs warned its clients to lock in trading profits before oil and other markets reverse. U.S. traded shares of Rio Tinto fell 2.3 percent to $72.10.

The concern expressed by Alcoa on Japan may be repeated by some other companies. The cautiousness that is associated with Japan will be a reoccurring theme throughout the earnings season, said Robert Pavlik, chief market strategist at Banyan Partners LLC in New York.

Brent crude futures pushed up to around $124.50 a barrel on Tuesday, edging up from a sharp fall, as the International Energy Agency issued a fresh warning that high prices could erode demand.

S&P 500 futures fell 6.8 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 48 points and Nasdaq 100 futures shed 10 points.

Looking at merger and acquisition news, two sources familiar with the matter told Reuters that Hewlett-Packard Co had considered buying business software company Tibco Software Inc until two weeks ago when talks fizzled.

On the economic data front, international trade, and import and export prices data are due at 8:30 a.m. ET.

In other corporate news, Chevron Corp , the second-largest U.S. oil company, said first-quarter exploration and production earnings would be higher than in the previous quarter.

Also, a former private equity executive was sentenced to 13 years and four months in prison for his role in a real estate investment fraud that federal authorities have called a $255 million Ponzi scheme targeting Orthodox Jews.

The Wall Street Journal reported that the Bank of America Corp's internal auditors are reviewing why its chief financial officer and chief accounting officer were not consulted before the bank disclosed to investors that its dividend increase had been rejected by regulators.

U.S. stocks mostly fell on Monday, with energy shares selling off on lower oil prices and concerns that company outlooks may fall short of expectations.

(Reporting by Angela Moon, Editing by Chizu Nomiyama)