Consumers should not eat shellfish from South Korea and retailers should stop selling it, federal and state regulators said Thursday.

The Food and Drug Administration yanked firms that transport Korean shellfish off its list of approved shippers on May 1 and said it may launch “a fairly extensive recall of the product” — specifically fresh, frozen or processed oysters, clams, mussels and scallops.

An agency analysis of the Korean shellfish program found unacceptable water pollution levels in shellfish-growing areas and periodic detection of norovirus, a common cause of acute gastroenteritis, or inflammation of the stomach and intestines.

Although the FDA lacks the authority to regulate retailers and their suppliers, it can seize contaminated products that are not removed from commerce. The agency has recommended that stores and distributors stop selling Korean shellfish. The advisory does not affect Korean crab or shrimp or any shellfish grown and produced domestically.

Only a small portion of molluscan shellfish sold in this country comes from South Korea, and no illnesses have been linked to that product this year. But in October, a norovirus outbreak sickened three people who ate contaminated oysters from South Korea and another illness also linked to Korean oysters occurred not long afterward. Nobody was hospitalized or killed. Norovirus is highly contagious, but it’s not usually life-threatening.

In a message to state authorities, the FDA stressed that the states can take any action that they deem appropriate to deal with the agency’s most recent warning.

Maryland officials contacted the one distributor in the state that they know handles Korean shellfish. The distributor put a hold on the products and asked its customers to stop selling the product and return it, said Alan Brench, chief of food emergency response and planning at the Maryland Department of Health and Mental Hygiene.

The distributor supplies about 30 mostly ethnic grocers and restaurants in the state, Brench said. Most of them are in the Baltimore-Washington corridor. Brench estimates that only a small amount of shellfish is affected in Maryland, about 10,000 pounds.

Local health departments in Maryland are also verifying that the seafood does not remain in retail stores, Brench said.

In Virginia, state regulators have contacted certified dealers in the state — most of them large restaurant chain suppliers — and barred them from shipping Korean shellfish, said Robert Croonenberghs, director of the shellfish sanitation division at the Virginia Department of Health.

The state has asked the dealers to voluntarily recall the product, and all have agreed to do so, Croonenberghs said. Some have voluntarily destroyed the seafood while others are waiting for direction from the FDA on how to proceed.

Virginia gets most of its oysters and other shellfish from local growers and other states, Croonenberghs said. But at least one container headed to Virginia with 40,000 pounds of frozen Korean oysters was stopped at port.

“I’m confident that what’s out on the market now is safe,” he said. “But if somebody has product in their freezer from Korea, don’t eat that.”

The District’s Department of Health said it is working on a strategy to deal with the issue.

Anyone who has recently bought molluscan shellfish should contact the retailer to inquire about its origin, health officials said. The label on seafood that comes in bags, cans or other packages should indicate the country of origin.