NEW YORK — Billionaire investor Carl Icahn, who last month demanded that Family Dollar Stores Inc. "be put up for sale immediately," has exercised call options to take ownership of the shares underlying his 9.4% stake in the Matthews, N.C.-based discount retailer.

Billionaire investor Carl Icahn, who last month demanded that Family Dollar Stores Inc. "be put up for sale immediately," has exercised call options to take ownership of the shares underlying his 9.4% stake in the Matthews, N.C.-based discount retailer.

At the time of his demand — which included a threat to mobilize to replace the company’s directors — Icahn held most of his stake in options to buy shares rather than in Family Dollar stock. That changed earlier this month, according to securities filings, when the 78-year-old Icahn exercised the options and spent $622 million for about 10.7 million shares.

Icahn disclosed his Family Dollar stake on June 6. In a June 19 letter to Howard Levine, the company’s chairman and chief executive officer, Icahn said: "We believe there would be significant interest from strategic and financial buyers who could recognize massive synergies from an acquisition of the company."

The letter prompted speculation in the business press that Family Dollar would succumb to a hostile takeover from activist hedge funds or scramble to forge a strategic partnership with a rival dollar chain operator.

The company in recent months has taken steps to improve its financial performance.