U.S. stocks pared earlier highs after the threat of Iranian oil entering the market pulled commodities lower. The International Energy Agency warned global oil markets could drown in oversupply this year as Iranian output begins to flood the market. Tiffany & Co. (TIF) shares were lower after the jeweler cut its forecast for the year. The retailer said challenging global economic conditions had pressured consumer spending, while a stronger U.S. dollar continued to reduce overseas sales. Twitter (TWTR) shares declined after the micro-blogging site suffered worldwide outages Tuesday morning with Europe the hardest hit. Visitors to the website, apps and third-party software had no or unreliable access throughout the morning. TheStreet's Keris Lahiff reports from Wall Street.