The operator of Carl’s Jr. and Hardee’s restaurants has accepted a higher $694 million buyout offer from an affiliate of private equity group Apollo Management VII LP.

The bid from Apollo affiliate Columbia Lake Acquisition Holdings Inc. topped a previous $619 million cash bid in February from affiliates of another private equity firm, Thomas H. Lee Partners. The transaction is valued at around $1 billion, including the refinancing of the Carpinteria fast food company’s outstanding debt.

Under terms of the deal laid out Monday, CKE stockholders would receive $12.55 in cash for each common share of CKE they hold. That’s a 41 percent premium to the company’s closing share price on February 25, and a 14 percent premium over the consideration provided by the merger deal previously entered into with affiliates of Thomas H. Lee Partners L.P. Completion of the transaction, first announced Saturday, is expected to occur by the end of the second quarter of fiscal 2011.

CKE accepted Thomas H. Lee’s offer of $11.05 a share in February. That offer included about $619 million in cash and the assumption of about $309 million in debt. Lee was among a trio of investment firms that bought Dunkin’ Brands Inc. in 2006.

Shares were down 47 cents, or 3.6 percent, to $12.48 in midday trading on the New York Stock Exchange.