Platinum Underwriters Group and its members have been affirmed the financial strength rating (FSR) of A (excellent) and issuer credit ratings (ICR) of "a" by AM Best Co.

Best also has affirmed the ICR of "bbb" of Platinum Underwriters Holdings Ltd. and debt ratings of Platinum and Platinum Underwriters Finance Inc. The outlook for all ratings is stable.

The ratings agency said that the ratings reflect the group's excellent capitalisation, strong operating results and established business position as a global, multi-line provider of reinsurance coverages, as well as the group's good financial flexibility, solid liquidity and sound enterprise risk management capabilities.

Somewhat offsetting these strengths were the challenges that have occurred in the global reinsurance market including rate softening and increased competition in recent years and the impact of the capital market crisis on total return measures, it said.

"The group has generated very strong underwriting results over the most recent five-year period with a five-year average combined ratio of 93.5 percent," said Best.

"From an earnings perspective, net investment income continued to contribute to the bottom line due to the group's growing invested asset base and sound operating cash flow measures."

Despite challenges related to natural catastrophes and investment market turmoil, Platinum generated a healthy 2008 earnings result with net income of $226 million, largely driven by favourable loss reserve development, added Best.