Treasury Secretary Timothy Geithner slammed Standard and Poor's on Sunday as showing "terrible judgement" in downgrading the US credit rating for the first time ever.

"I think S&P has shown really terrible judgement and they've handled themselves poorly, and they have shown a stunning lack of knowledge about basic US fiscal budget math and I think they came to exactly the wrong conclusion," Geithner said in an interview with NBC News.

His comments came amid growing suspense over the impact on world financial markets of the downgrade of S&P's rating for US Treasuries from AAA to AA+.

Geithner took exception to S&P focus on the deep bipartisan divide in Washington over fiscal policy, saying, "Our country is much stronger than Washington.

"We have a very resilient economy. We're a very strong country and I have enormous confidence in the basic regenerative capacity of the American economy and the American people," he said.

Earlier, the White House said Geithner was staying on US Treasury secretary as some Republicans called for his resignation in the wake of the downgrade.