Currently, the S&P maintains the US' top AAA credit rating, but said there is a one-in-three chance it could cut its long-term credit rating within two years if US policy makers fail to deal with rising budget deficit and debt. Guan said that the US economy was still worsening after Dagong downgraded the country's rating last year, due to the military missions in Libya, as well as the rising defense budget and fiscal expenditures.

China's holding of dollar assets is risky, he warned. "We are closely tracking the performance of US government bonds and considering a further adjustment based on current conditions."

Moody's Investors Service Inc, another leading ratings agency, warned of the same debt risk in the United States. "Moody's rating for the US is AAA and remains stable, but an upward debt trajectory and increasing fiscal pressures increase the likelihood of an outlook change within the next two years," said Steve Hess, Senior Credit Officer with Moody's.

But Moody's was more positive over the future development of the US economy. In its latest weekly credit outlook report, the ratings agency wrote that "despite these uncertainties, we view the changed parameters of the debate with broadly similar goals as to government debt levels as a turning point that is positive for the long-term fiscal position of the US federal government."

Some Chinese economists were also optimistic on the US debt risk. Yang Tao, a researcher with the Chinese Academy of Social Sciences, said there is little chance for a US debt crisis, unless all of the bond holders sold their US Treasury bonds, which would hurt the interests of all nations.

Lu Zhengwei, chief economist with Industrial Bank Co Ltd, said that the US debt repayment capability will become better once the United States posts a better-than-expected economic recovery. Lu also called for the Chinese government to urge the US administration to take full responsibility for its debt, as well as the global economic development and financial system.

Some economists noted that China should pay close attention to the US credit conditions and diversify the investments of its foreign reserves.