Alimentation Couche-Tard Inc., Canada’s largest convenience store operator, announced this morning it has launched a cash tender offer of $36 per share in a takeover bid for Ankeny-based Casey’s General Stores Inc., as Couche-Tard attempts to expand its retail presence in the United States.

Casey’s officials said in a press release that it has advised its shareholders not to take any action on the offer until the company’s board of directors reviews the offer within the next 10 days.

Casey’s board of directors in April unanimously rejected a bid for the same per-share amount. Couche-Tard, which already has 3,600 stores in the United States, said at the time it would take its offer directly to Casey’s shareholders if the board failed to reconsider its rejection.

The tender offer, worth an estimated $1.85 billion, is scheduled to expire on July 9, unless extended.

“It remains our strong preference to enter into a negotiated transaction with Casey’s and it is unfortunate that the Casey’s board has rejected our $36 per share all-cash offer without any discussion or negotiation,” said Couche-Tard’s CEO Alain Bouchard, in a press release.

Couche-Tard said if Casey’s refuses to enter into a merger agreement, it will nominate a slate of nine directors for election to Casey’s board at Casey’s 2010 shareholder meeting.

Casey’s officials said in a release that “if and when Couche-Tard nominates directors, the board will evaluate the submission and candidates consistent with the company’s bylaws.”

Couche-Tard’s offer price represented a 14 percent premium over Casey’s closing price of $31.59 on the Nasdaq Stock Market on April 8, a day before the bid was announced, the company said.

Shares of Casey’s, which has about 1,500 convenience stores in the Midwest, closed Tuesday at $36.34 and have for the most part traded above the offer price since the bid was announced, suggesting investors expect a higher offer to eventually emerge, Reuters reported.