White Mountains Solutions Holding Company has signed a definitive agreement for acquisition of a runoff subsidiary of US insurer, American International Group (AIG).

As part of the agreement, White Mountains will acquire American Fuji Fire and Marine Insurance Company.

Subjected to customary closing conditions and regulatory approval from the Departments of Insurance in Illinois, the transaction is expected to close during the first quarter of 2013.

The company has recently completed acquisitions of Physicians Insurance Company and Citation Insurance Company from PICO Holdings and two AIG runoff subsidiaries, including American General Indemnity Company and American General Property Insurance Company.

White Mountains is a financial services firm, offering property and casualty insurance and reinsurance products through its subsidiaries.