NEW YORK (AP) — Walgreen Co. said Monday it is offering to continue filling prescriptions for military members, retirees, and their families under a new deal with Express Scripts Inc., but the pharmacy benefits manager said the offer was not good enough.

Express Scripts, one of the largest pharmacy benefits managers in the U.S., pays drugstores like Walgreen to fill prescriptions. A three-year contract between the companies expires Dec. 31, and they have not been able to negotiate a new deal. Walgreen and Express Scripts said in June they will stop doing business when the contract ends, meaning most people whose drug benefits are handled by Express Scripts won't be able to pick up prescriptions at the biggest chain of drugstores in the country.

Walgreen said Monday it has offered to continue filling prescriptions for members of the Defense Department's Tricare health care program, which is for military members, retirees, and families. Express Scripts handles the prescription drug benefit for Tricare. Walgreen said it is willing to guarantee it will match or beat the average cost of adjusted prescriptions filled at any other pharmacy in the Tricare network, which it said has about 6 million beneficiaries.