ST. LOUIS — Missouri Attorney General Chris Koster sued Walgreen Co. on Tuesday, accusing the nation’s largest pharmacy chain of overcharging customers and using deceptive display advertising and pricing schemes.

Koster filed the suit in Kansas City and announced details at a news conference in St. Louis. The suit seeks an injunction forcing the Chicago-based chain to stop the allegedly deceptive practices. It also seeks unspecified fines and damages.

“My concern is this is not sloppiness — this is a business practice that is consciously intending to steal from sick people that go into Walgreens, from old people that go into Walgreens,” Koster said.

Walgreen spokesman Jim Graham said the company has not seen the suit and declined comment.

The Missouri investigation began after many consumers complained that display tag prices didn’t match up with what they paid at checkout, Koster said. His office sent undercover investigators to eight Walgreen stores in five Missouri cities — St. Louis, Kansas City, Springfield, Jefferson City and Osage Beach — in June and July.

What they found, Koster said, “was appalling.”

Koster cited several ways in which consumers were overcharged: outdated price displays for sale items; confusion created by multiple prices displayed for the same item; displays offering discounts for rewards members, but with no discount given; and full prices charged for items in clearance bins.

Of 205 items purchased by investigators, 43 had price discrepancies ranging from a few cents up to $15, Koster said.

In January, Walgreen agreed to pay more than $1.4 million in civil penalties and to establish a price guarantee program in California after four Bay Area counties sued over price discrepancies. And in March, the company paid nearly $30,000 to settle claims that it scanned inaccurate prices and didn’t post refund notices at stores in Wisconsin.

“I expect this will not be the last state to take on Walgreens,” Koster said.