The fiscal cliff agreement does not mean US decision-makers have found a solution for the country's financial problems, as politicians have been urged to tackle the budget deficit.
Two leading ratings agencies have called for policymakers to take steps to balance the largest global economy's books.
Standard and Poor's indicated Washington DC's governance has grown less robust and that it is time to take action to bring about stability.
Rival agency Moody's stated that lawmakers need to take further action to lower the deficit, which has topped $1 trillion (£615 billion) for four consecutive years.
Moody's said that if the government fails to reduce this amount, the government's top AAA credit rating could be at risk.
At close of play on Wall Street last night (January 2nd), the technology-heavy Nasdaq rose by more than three per cent to 3112.2 points, while the Dow Jones climbed by 2.3 per cent to 13412.5 points.
Learn about the US markets and CFD trading at City Index.