Rating agency Standard and Poor's has raised its credit outlook for the U.S. economy from negative to stable, BBC News reported.

In August 2011, S&P downgraded the U.S. rating one notch from AAA to AA+, but now believes further downgrades are less likely as the economy continues to recover.

The news saw the U.S. dollar strengthen 1.3% against the Japanese yen, and 0.2% against the euro. But S&P is still concerned about the high levels of U.S. debt.

The move came as the Paris-based Organisation for Economic Cooperation and Development (OECD) said that economic growth in the U.S. and Japan was outstripping that of the eurozone.

But most U.S. analysts remained cautious about the upgrade and the equity markets opened only slightly higher.

Omer Esiner, chief market analyst at Commonwealth Foreign Exchange in Washington DC, said: "The revised rating is positive news for the dollar but I do not see it being a major catalyst.

"This is just the latest indication that we are seeing a broad stabilisation and improvement in the economy and ultimately the government's fiscal position is improving, albeit slowly."

Rival rating agencies Moody's and Fitch have both kept their AAA ratings for the U.S.