Liquid milk sold by three leading companies is contaminated with melamine, tests showed yesterday, the day when the number of infant deaths caused by the chemical rose to four.

The fourth death was reported from the Xinjiang Uygur autonomous region. Two kids in Gansu and one in Zhejiang had fallen victim to contaminated milk earlier. A total of 6,244 infants who were fed contaminated milk food produced by Sanlu Group have been diagnosed with various urinary tract problems, including kidney stones.

Police in Shijiazhuang, where Sanlu is based, said 12 people were arrested yesterday for their alleged involvement in the milk food scandal, taking the total number of arrests to 18.