Standard & Poor's has cast doubt on Prime Minister Shinzo Abe's ability to repair Japan's tattered finances less than two weeks away from a snap election, after Moody's downgraded the country's sovereign debt rating.

Abe's decision to delay a sales tax increase by 18 months may help the economy in the short term, but there is still no guarantee taxes will rise because the political dynamic could change after the election, Takahira Ogawa, director of sovereign ratings at S&P, said in a recent interview.

The growing reservations about Japan come at an awkward time for Abe, who has called a Lower House election Dec. 14 that has become a vote on whether he has done enough to fundamentally improve the prospects for economic growth.