"Hopefully it is unlikely that we go past October 17 and fail to raise the debt ceiling, but even if that does happen, then we think that the U.S. Treasury is still going to pay on those Treasury securities," he added.

"It is extremely unlikely that the Treasury is not going to continue to pay on those securities," Moody's CEO Raymond McDaniel said in an interview with CNBC.

If the U.S. government defaults on its debt, it could have negative consequences for financial markets worldwide.

As the U.S. government shutdown looked set to continue for a sixth day on Monday, concerns that the ongoing political stalemate will cause the Treasury to miss its October 17 deadline for raising the $16.7 trillion borrowing limit, remained at fever pitch.

The CEO of credit rating agency Moody's ruled out the chance of a U.S. government default, even if an agreement over raising the debt ceiling is not achieved by mid-October.

Thus far, financial markets have displayed a relatively muted reaction to the government shutdown, which began last Tuesday after Democrats and Republicans failed to renew the federal budget into a new fiscal year. Wall Street's S&P 500 is up roughly 0.5 percent since the beginning of the shutdown to Friday's close, for example.

McDaniel attributed the markets' seemingly complacent reaction to the relatively fresh memory of the 2011 political stalemate over the debt ceiling issue, which was ultimately resolved.

"[It] feels a lot like we've seen this movie before," said McDaniel. "Ironically because we have had this experience in the recent past [it] gives people more of a sense of calm than perhaps they should have."

(Read more: Debt default would be catastrophic: Erskine Bowles)



"The fact that the market is reacting more calmly is good, but to the extent that policy makers are going to act when stress or distress reaches a certain level, the market can play a role in indicating that," he added.

U.S. Treasury Secretary Jack Lew gave a much less calm depiction of the scenario in an interview with NBC's Savannah Guthrie.

Reiterating his previous statement that by October 17, the Treasury will have only $30 billion left in the coffers, he warned that U.S. politicians were playing with fire.

"$30 billion is a dangerously low level of cash. And we're on the verge of going into a place we've never been, not having cash to pay our bills," he said.

Lew said the U.S. Government actually hit the debt ceiling limit in May, forcing him to use "extraordinary measures" to create additional headroom. He said the capacity to use these measures had now expired and said he had "nothing else in the drawer."

"So the reality is that if we run out of cash to pay our bills, there is no option that permits us to pay all of our bills on time," he added.

(Read more: Short-term US debt under pressure on default fears)



Meanwhile, House Speaker John Boehner has warned that the U.S. is on the path to the credit default in an interview in ABC's 'This Week' on Sunday.

"My goal here is to have a serious conversation about those things that are driving the deficit and the debt up. The President's refusal to sit down and have a conversation about this is putting our nation at risk of default... it's the path we're on," he told ABC.

President Barack Obama has refused to negotiate over raising the debt ceiling out of concern that it would give credence to the Republicans' tactic of threatening default whenever their demands are not met.

Moody's holds a triple-A rating for U.S. government debt with a stable outlook. S&P meanwhile, stripped the U.S. of its triple-A rating in August 2011 and now holds a AA-plus rating with a stable outlook. Fitch rates the country AAA with a negative outlook.

— By CNBC's Katie Holliday: Follow her on Twitter @hollidaykatie

