MILAN, May 31 (Reuters) - Italy's biggest insurer Assicurazioni Generali on Monday said it would launch a buyout offer on smaller rival Cattolica to further cement its domestic leadership.

Generali, which already owns a near 24% stake in Cattolica, said it would pay 6.75 euros a share offering a premium of 15.3% on Cattolica's closing price on Friday.

(Reporting by Valentina Za, editing by Giulia Segreti)