Four more Japanese baby formula brands have been found to contain excessively low levels of iodine that could affect brain development, after six milk powder products were discovered to contain insufficient amounts last week, Hong Kong's food safety center announced.

The products — two of which are produced by Morinaga Milk Industry Co., one by Meiji Co. and the other by Wakodo Co. — contained iodine levels of less than a third of the standard recommended by the World Health Organization, the center said Friday.

Morinaga's products are marketed for infants up to 12 months old, Meiji's for those up to 36 months and Wakodo's for babies up to 9 months.

On Wednesday, Hong Kong's government said six milk power brands for infants aged up to 9 months were deficient in their iodine content, including four produced by Japanese manufacturers: Wakodo, Morinaga, Meiji and Snow Brand Milk Products Co. The other two are made by France's Physiolac and Friso of the Netherlands.

Local maternity clinics are currently conducting blood tests on babies up to 8 months old to check for any irregularities.

Morinaga and Asahi Group Holdings Ltd., which owns the Wakodo brand, argue their products are safe and produced in line with Japanese regulations, which they say do not allow companies to supplement their products with iodine.

Parents in Hong Kong, and especially in mainland Chinese, have favored Japanese milk powder over local brands since melamine-tainted milk products in 2008 killed six children and sickened thousands in China.