At least four people in the United States have become sick after eating South Korean seafood - three in October and one in December, the FDA said on Thursday.

The regulatory warning spans the range of fresh, canned and processed seafood products that contain the seafood types known as molluscan shellfish that entered the United States before May 1, when the FDA first removed them from an interstate list of certified shellfish shippers.

An FDA official said U.S. representatives are in talks with South Korean officials about the problem that involves polluted fishing waters where the seafood was harvested.

An official with the South Korean embassy in Washington had no comment.

Some food companies have already removed the products from their distribution networks. But the agency said not all have complied and it issued the warning in an effort to reach retailers distributors and food service operators.

"These products and any products made with them may have been exposed to human fecal waste and are potentially contaminated with norovirus," the FDA said in a statement.

South Korean shellfish represent only a tiny fraction of the oysters, clams, mussels and scallops sold in the United States.

Norovirus causes gastroenteritis, a disorder characterized by nausea, vomiting, diarrhea, stomach cramps and other symptoms that occur within 12-48 hours of exposure and last up to three days.

The FDA took action after determining that a South Korean program to safeguard shellfish contamination did not meet U.S. standards for sanitary controls.

The agency advised consumers to check seafood labels and contact seafood vendors, if they are concerned about products they have purchased, and throw out any found to be from South Korea.

(Reporting By David Morgan, Anna Yukhananov and Salimah Ebrahim; Editing by Bob Burgdorfer and Tim Dobbyn)

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