HAMILTON, Bermuda—Rating agency Standard & Poor’s Corp. has assigned A- counterparty credit and financial strength ratings to Validus Reinsurance Ltd., a unit of Bermuda-based Validus Holdings Ltd.

In addition to the new ratings, New York-based S&P upgraded Validus’ counterparty credit rating to BBB from BBB-, the rating agency said in a statement Tuesday.

Last September, Validus completed its $1.77 billion acquisition of IPC Holdings Ltd., which it won in a bidding battle with Bermuda-based reinsurer Max Capital Group Ltd.

S&P credit analyst Tracy Dolan said in the statement the upgrade reflects “Validus’ successful integration and retention of the profitable portions of IPC’s book of business, which has resulted in an enhanced competitive position through the significant expansion of its presence in the global property catastrophe market and a larger balance sheet.”