Global credit rating agency Standard and Poor's or (S&P) has lowered its long-term rating outlook on the United States to “negative” from “stable” for the first time.

S&P also said on Monday that the U.S. could risk losing its AAA credit rating if policy makers fail to agree on a plan by 2013 to reduce budget deficits and the nation’s debt.

In response, the White House protested the recent revision, saying the agency’s decision was a political assessment that had underestimated Congress’s capacity to reduce budget deficits.

S&P’s move comes after other credit rating agencies, including Moody's Investors Service and Fitch Ratings, positively evaluated Washington’s plan to cut budget deficits.

Stock prices fell sharply around the world following the recent projection.