Earlier, Fitch Ratings said Kim's death did not merit a negative move on South Korea's A+ rating, adding that it was too early to say that risks had materially increased.

Last month, Fitch had revised its outlook on the rating to positive from stable.

South Korean assets took a hit as financial markets speculated about what might happen next in the isolated state, whose collapsing economy and bid to become a nuclear weapons power pose major threats to northeast Asia.

S&P said in a statement: "Our ratings on South Korea take into account temporary uncertainties associated with North Korean security risks as well contingent liabilities arising from a possible reunification of the North and South."

It said that although the death of the North Korean leader raised uncertainties, South Korea's credit standing would be little changed in the event of a smooth leadership succession.

But it warned South Korea's rating or outlook could be revised if the succession plan was not smoothly implemented or if there were other signs of political instability.