Global ratings agency Standard & Poor's warned Thursday it may cut India's sovereign rating to "junk" status if the next government cannot turn around the weak economy.

S&P's statement raises the stakes for the general elections due by next May amid speculation about a fractured outcome which could lead to an unwieldy coalition including many small regional parties.

India's economic growth has fallen to a decade low amid political gridlock and a string of corruption scandals that have made the Congress-led government deeply unpopular.

The ratings agency said it was maintaining India's investment-grade rating due to its "institutional strengths and high international (financial) reserves", but noted a marked slowdown in economic growth.

S&P said its ratings outlook remained negative, "indicating we may lower the rating to speculative grade next year if the government that takes office after the election does not appear capable of reversing India's low economic growth".

The election will pit secular Congress hopeful Rahul Gandhi, scion of the Gandhi-Nehru dynasty, against the charismatic but divisive Hindu nationalist Bharatiya Janata Party leader Narendra Modi.

While opinion polls suggest the political wind is behind Modi, liked by business for his investment-friendly policies, analysts say regional parties will have greater leverage than ever before due to a shift in voter loyalties.

India's current S&P rating of 'BBB-' is one notch above "junk."