TOKYO, March 23 (Reuters) - Tokio Marine Holdings Inc ( TKOMF ) said on Monday it would form a strategic partnership with Warren Buffett's Berkshire Hathaway ( BRK/A ) by initially selling a 2.49% stake through a third-party allotment of treasury shares.

The insurer said it would use the proceeds of up to 287.4 billion yen ($1.80 billion) to buy back its own shares to prevent dilution for existing shareholders.

Following the initial share allocation to Berkshire's core reinsurance entity, National Indemnity, any additional acquisition of Tokio Marine's ( TKOMF ) shares are expected to be made primarily through the open market, Tokio Marine ( TKOMF ) said in a filing.  National Indemnity will agree not to buy more than 9.9% of Tokio Marine's ( TKOMF ) outstanding shares without prior approval from the latter's board, the statement said.

($1 = 159.4100 yen)