Jamie Dimon cautions against panic as U.S. nears debt default.

JPMorgan Chase CEO Jamie Dimon has warned that panic will grip markets as the U.S. approaches a possible default on its sovereign debt, which he called "potentially catastrophic" for the country. While he expects the worst-case scenario to be avoided, Dimon said that if it gets to the panic point, people have to react, and it could affect other markets around the world. JPMorgan has been preparing for the risk of an American default, and Dimon exhorted politicians from both major U.S. parties to compromise and avoid a ruinous outcome.