Honey Smacks has been linked to 100 salmonella infections in 33 states, according to a Centers for Disease Control and Prevention update from Thursday. Thirty people have been hospitalized.
Kellogg's voluntarily recalled the cereal on June 14, but the FDA said that it has become aware that some retailers are selling the product almost a month after the recall.
"Retailers cannot legally offer the cereal for sale and consumers should not purchase Kellogg's Honey Smacks cereal," the FDA said in the press release.
The most recent case reported that symptoms began July 2.
Both the CDC and the FDA told retailers that they should not sell or serve recalled Honey Smacks and warned consumers not to buy the cereal in stores and to discard any boxes of Honey Smacks they have at home.
FDA investigators found that a third-party Honey Smacks manufacturing facility was responsible for the outbreak. The facility was no longer producing the cereal as of Thursday, the FDA said in its Thursday update.
"We continue to work with the FDA and the third-party manufacturer to determine how this happened to ensure it doesn't happen again," said a spokesperson from Kellogg's in an email to CNBC. "Kellogg is asking that people who purchased potentially affected product discard it and contact the company for a full refund."