BEIJING - China's top quality watchdog said Monday that the eating of mildewed feed by cows has caused excessive levels of a cancer-causing toxin in milk products made by two producers in the latest food safety scare involving heavyweight Mengniu Dairy Group in China.

Excessive levels of aflatoxin were discovered in two batches of milk products made by the Fujian-based Changfu Dairy and Mengniu's plant in the southwestern province of Sichuan, according to test results released by the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ).

An AQSIQ official said Monday the toxin had originated from cows eating mildewed feed, citing reviews by experts. The toxin would disappear if the animals stop eating the rotten feed, the official said.

The government agency has sent four working groups this year to test the quality of finished products made by 128 companies in 21 provinces in the country. The tests covered 200 kinds of milk products.

Of the 200 kinds of products tested, 198 were qualified, according to the official.

The watchdog had ordered local quality bureaus to ask the two companies to recall and destroy the tainted products.

Mengniu Dairy Group, China's largest milk producer, said in a statement on its website Monday that the problem was discovered before the disqualified milk was sold on the market.

The company also made an apology to the public through the statement.

Aflatoxin is produced by a fungus that commonly grows on crops such as grain and peanuts. High levels of the toxin may lead to cancer in some animals.