CKE Restaurants Inc , owner of the Hardee's and Carl's Jr. hamburger chains, said it received an alternative takeover offer, which could lead to a superior proposal, sending its shares up 6 percent in pre-market trade.

The new offer did not include evidence of a committed financing and is subject to several conditions, CKE Restaurants said in a statement.

The fast food chain had in February agreed to be bought by private equity firm Thomas H. Lee Partners for $619 million cash and had 40 days to seek superior offers.

That go shop provision expired on Tuesday.

On Tuesday, Porter Orlin, a New York-based investment manager holding almost 2.3 million shares in CKE, wrote a letter to the company, expressing strong dissatisfaction with Thomas H. Lee Partners' plan to take the company private.

The company has not changed its recommendation on its pending merger with affiliates of Thomas H. Lee Partners, CKE Restaurants said.

Shares of Carpinteria, California-based CKE were up $0.64 at $11.72 Wednesday in trading before the bell. They closed at $11.08 Tuesday on the New York Stock Exchange.

(Reporting by Renju Jose in Bangalore; Editing by Jarshad Kakkrakandy)