Melamine was found in Snickers Peanut Funsize and M&Ms chocolate milk made by Mars, as well as KitKat wafers made by Nestle and a biscuit manufactured by Lotte Confectionery Co., the Food and Drug Administration said in a statement Saturday.
The test results raise the number of known melamine-tainted food products imported to South Korea from China to 10.
About 430 Chinese-made products using dairy ingredients have already been pulled from store shelves and put into storage pending tests.
The U.S. Food and Drug Administration has said small amounts of melamine -- less than 2.5 parts per million -- are not harmful in most foods, except baby formula.
The South Korean tests found 1.78 parts per million of melamine in Snickers bars, 2.38 parts per million in M&Ms, 2.89 parts per million for KitKats, and up to 3.36 parts per million in the Lotte biscuits.
Lotte and Mars Korea said they were withdrawing their products. Comments from Nestle Korea were not immediately available.
Last week, Seoul suspended imports of all Chinese-made foods using dairy ingredients.
In China, melamine-tainted milk formula has sickened more than 54,000 children, mainly with kidney problems, and is blamed for the deaths of at least four infants.
Melamine is believed to have been added to Chinese milk to artificially boost its apparent protein level.