After completing the $6.2 billion acquisition of Seattle-based Safeco Corp. yesterday, Liberty Mutual’s Issuer Default and Insurer Financial Strength ratings were downgraded by Fitch Ratings today.

Liberty Mutual’s IDR ratings were downgraded to ‘BBB’ from ‘BBB+’, and the IFS ratings were lowered to ‘A-‘ from ‘A.’

The actions reflect Fitch's concerns about “the post-acquisition capitalization of Liberty Mutual’s and Safeco’s operating companies, integration and execution risk derived from the acquisition, first half 2008 premium growth that Fitch views as generally higher than that of peers, and moderately higher consolidated financial leverage resulting from financing the transaction,” the company said.