Canada-based Alimentation Couche-Tard Inc. upped the ante today in its attempt to buy Casey’s General Stores Inc., telling shareholders it will pay $38.50 a share for all outstanding stock, up from its previous offer of $36.75 a share.

On Tuesday, Ankeny-based Casey’s said it had completed a stock buyback in which it will pay $38 a share for nearly 26 percent of its stock. The announcement prompted one analyst to predict that Couche-Tard would have a difficult time buying Casey’s in the wake of the repurchase.

Also on Tuesday, Couche-Tard announced that it had extended its tender offer to Sept. 30. That offer, at $36.75 a share, was set to expire Monday. In making that announcement, Couche-Tard said it had acquired nearly 1.1 percent of Casey’s stock.

Alain Bouchard, president and CEO of Couche-Tard, said in a statement today that his company followed the lead of Casey’s shareholders who indicated via the company’s stock buyback that they considered $38 a share a reasonable price for the company.

“In Casey’s self-tender offer, the shareholders of Casey’s made clear their views on the value of Casey’s,” he said. “The fact that a majority of the then-outstanding shares of Casey’s were tendered at $38 per share demonstrates that our revised offer to acquire 100 percent of the outstanding shares of Casey’s for $38.50 per share in cash is compelling.”

Casey’s shares were trading at $38.84 at 10 a.m. Iowa time after closing Tuesday at $37.62.

Couche-Tard’s bid is valued at nearly $2 billion, including $528 million in Casey’s debt, much of it acquired as a result of the stock buyback. An analyst said Tuesday that as a result of the repurchase plan, the real cost to buy Casey’s stands at about $38.90 a share, including the assumption of debt.

Casey’s plans to buy 13.2 million shares at that price. After the purchase is completed, Casey’s said it expects to have total of 37.8 million shares of stock.

After Couche-Tard announced the higher bid today, Casey’s issued a statement asking shareholders to delay taking action until the board makes a recommendation.

Couche-Tard announced in April that it wanted to take over Casey’s in an attempt to increase its substantial presence in the convenience store industry. The company, based in Laval, Quebec, operates more than 5,800 stores, many acquired through mergers, in Canada and the United States.

Casey’s board has rejected all overtures from Couche-Tard.

Both sides meet today in federal court in Des Moines, where a judge will hear arguments in Casey’s attempt to block the takeover. Casey’s argues that Couche-Tard violated federal securities law when it made a $10 million profit by selling Casey’s shares shortly after announcing it planned to buy the company.

Couche-Tard has countersued, attacking the constitutionality of state laws that Casey’s board used in creating a poison pill to block the hostile takeover.

The Canadian company also plans a proxy fight to control Casey’s board. Casey’s annual shareholders meeting is Sept. 23.