U.S. stock market opened slightly higher on Tuesday after Russian President Vladimir Putin said he did not seek to partition Ukraine, while signing a treaty to annex Crimea. Reaction to a pair of economic reports that were in line with expectations was muted, while all attention turned to the Federal Reserve's two-day policy-setting meeting, which is set to begin on Tuesday. The S&P 500 opened 2.3 points, or 0.2% higher at 1,862.14. The Dow Jones Industrial Average gained 22 points, or 0.2%, to 16,280.55. The Nasdaq composite rose by 0.2%, at 4,289.27