Traces of the potentially deadly chemical melamine have been found in a wide range of dairy products, with alerts over tainted products now spreading beyond mainland China.
Mars said while it was complying with the South Korean request, the melamine levels detected were too small to pose a health risk, and called for a standard reporting limit of the industrial chemical across Asia.
"Minute traces of melamine are commonly found throughout the global food chain and melamine levels below 2.5 ppm are not deemed to indicate adulteration with melamine," Mars said in a statement.
There was no immediate comment from Nestle Korea.
A KFDA official said South Korea did not allow any level of melamine in food.
Peter Ben Embarek, a food safety expert from the World Health Organisation (WHO) said many countries had only recently fixed limits for melamine in food as "melamine has nothing to do with the food chain".
The Chinese government has said it will introduce a new food monitoring system in response to the crisis - the latest in a series of safety scandals to rock China's food and manufacturing industries.
The chemical was added to milk before being sold to dairy manufacturers in a bid to falsely boost protein readings, Chinese authorities have said.
A fourth Chinese milk product has been withdrawn from sale in Australia after tests revealed it was tainted with melamine, Food Standards Australia New Zealand said in a statement.
"Consumers are advised not to consume Kirin milk tea made in China," the organisation said.
Chinese authorities say melamine was put into the milk powder to make it appear the product had more protein.
The chemical, normally used to make plastics and glues, is rich in nitrogen, an element often used to measure protein levels, and so can be used to disguise diluted milk.
It is being blamed for causing kidney stones in the affected babies, a condition that is rare in infants but which causes a range of health risks.
The Australian food watchdog has already recalled White Rabbit sweets and Chinese-made Cadbury chocolate Eclairs, while importers of Lotte Koala Biscuits have undertaken a precautionary withdrawal of the product.
A Japanese importer, meanwhile, began recalling Chinese chocolates suspected of being contaminated with melamine.
The western Japanese city of Osaka said a test showed the chemical had been detected in "Chocolate Pillows" imported from China by Osaka-based NS International.
While there had been no reports of health problems, the city ordered the importer to recall nearly 86,000 packages of the chocolates on the grounds that the company may have violated the food sanitation law.
China is struggling to limit the damage to its food safety reputation as a growing number of countries have decided to suspend imports of Chinese milk products or withdraw them from sale over the scandal.
The European Union recently banned all imports on Chinese milk-related products for children such as biscuits and chocolate on top of a long-standing embargo on Chinese dairy products such as milk and yoghurt.