By Warren Strobel MUSCAT (Reuters) - Iran, the United States and European Union will hold an unscheduled second day of talks on Monday on disagreements blocking resolution of a dispute over Tehran's nuclear program, a U.S. official and Iranian state media said. With two weeks to a deadline for a comprehensive accord, Iranian Foreign Minister Mohammad Javad Zarif, U.S. Secretary of State John Kerry and EU envoy Catherine Ashton met in Oman's capital Muscat on Sunday to address a decade-long confrontation that has raised the risk of a wider war in the Middle East. ...