JPMorgan Chase & Co. CEO Jamie Dimon says a U.S. default would be catastrophic for the U.S. and the global economy.

Speaking with journalists Thursday morning after releasing second quarter earnings, Dimon said: "No one can tell me with certainty that a U.S. default wouldn't cause catastrophe and wouldn't severely damage the U.S. or global economy."

Dimon's comments come a day after Moody's Investors Service threatened to lower the United States' government's triple-A bond rating because the White House and Congress are running out of time to raise America's $14.3 trillion borrowing limit and avoid a default.

Dimon said it would be irresponsible to take chances and that it was imperative to resolve the debt ceiling issue quickly.

"Why take that chance?" he said. "I wouldn't take that chance."