A.M. Best Co. has upgraded the financial strength ratings to A+ (Superior) from A (Excellent) for Keyport Life Insurance Company, based in Lincoln, R.I., and its life insurance subsidiaries and removed the companies from under review.

The rating actions follow the recently completed acquisition by Sun Life of the insurance business of Liberty Financial Companies, Inc.

A.M. Best has also affirmed the group financial strength rating of A++ (Superior) for Sun Life Assurance Co. of Canada, and its strategic subsidiaries, Sun Life Assurance Company of Canada (U.S.) and Sun Life Insurance and Annuity Company of New York. Additionally, A.M. Best has affirmed Sun Life’s existing debt ratings.

Sun Life purchased the assets of Keyport and its two wholly owned life insurance subsidiaries as well as the Independent Financial Marketing Group, a third-party marketer of insurance and investment products to retail customers through banks in the United States.

Keyport is a specialty insurance company providing a diversified line of fixed, equity-indexed and variable annuity products sold through multiple distribution channels, including banks, agents and brokerage firms. A.M. Best views this acquisition as a key component of Sun Life’s growth strategy in the U.S. market; complementing Sun Life’s core wealth management business, increasing its competitive position and enhancing its distribution capabilities through increased cross-selling opportunities and expansion into bank distribution channels.

The ratings agency says it believes the strength and breadth of Sun Life’s operations, including its mutual fund franchise, will improve Keyport’s competitive positioning and provide sufficient capital for growth.