The Federal Reserve Board approved First Financial Bancorp.'s acquisition of Greensburg, Ind.-based MainSource Financial Group Inc.

It also approved MainSource Bank's merger into First Financial Bank.

The $1.0 billion, all-stock transaction pushes Cincinnati-based First Financial over the $10 billion regulatory threshold. The parties have secured state regulatory and shareholder approvals. They were also required by the U.S. Justice Department to divest themselves of five branches following the deal's close, which is now scheduled for April 1.