(Bloomberg) ? The debt and financial strength ratings of ACE Ltd., a Bermuda-based insurer, were left unchanged by Standard & Poor?s after a six-week review.

S&P said yesterday it kept Ace?s senior debt rating at BBB+ and its financial strength ratings at A+. Financial strength measures an insurer?s ability to pay claims.

The rating company began its review on January 6, when ACE said an increase in its reserves for asbestos claims cut fourth- quarter earnings by about $300 million. Ace spokesman Robert Grieves said the company was pleased that S&P maintained its ratings. S&P left a negative outlook on ACE?s ratings, meaning S&P is more likely to cut than raise them over the next several years. S&P said Ace may not be charging enough for some policies and may be setting aside too little to pay claims. That could diminish future earnings, it said.

Shares of the company fell 37 cents, or 0.8 percent, to $45.54 at 10:59 a.m. in New York Stock Exchange composite trading. They have risen 1.7 percent in the past 12 months, compared with a 3.4 percent gain in the KBW Insurance Index.