(Iin U.S. dollars unless noted)

TORONTO (Reuters) - Alimentation Couche-Tard is willing to sweeten its $2 billion offer forU.S.-based Casey's General Stores, Canada's largestconvenience store operator said in an open letter to Casey'sshareholders Thursday.

"If Couche-Tard is granted access into a fair process andhas the opportunity to conduct a confirmatory due diligencereview of Casey's on the same playing field as 7-Eleven, wewould be willing to consider further increasing our offer,"Couche-Tard Chief Executive Alain Bouchard wrote.

Casey's confirmed earlier this month that the Midwest-basedconvenience store chain was in talks with Japan's 7-Eleven,which made a non-binding offer of $40 a share. 7-Elevenoperates more than 31,400 stores around the world.

Montreal-based Couche-Tard, which last offered $38.50 ashare, said that its offer for Casey's was fully financed andthat it expected to keep most, if not all, of the employees ofCasey's in place.

Casey's has consistently dismissed Couche-Tard's overturesas significantly undervaluing the company and has urgedshareholder to reject the hostile bid.

($1=$1.03 Canadian) (Reporting by Solarina Ho)