Babies have been suffering kidney stones - rare in young children
A Chinese firm accused of selling milk powder that has made babies unwell was warned in August over the safety of its product, its partner and co-owner says.
New Zealand-based dairy giant Fonterra said it had urged China's Sanlu Group to recall the tainted powder six weeks before Sanlu took adequate action.
The Fonterra farmers' co-operative owns a 43% stake in Sanlu.
More than 400 babies in China have been taken ill after using milk contaminated with the industrial chemical, melamine.
Melamine is used to make plastics and is banned from food. Ingesting it can lead to the development of kidney stones.
At least one child has reportedly died in China as a result of using the contaminated milk, which the firm recalled from sale on Thursday.
In a statement released on Sunday, Fonterra said it had urged Sanlu's board to recall the milk powder as soon as it learnt of the contamination - on 2 August.
"From the day that we were advised of the product contamination issue in August, Fonterra called for a full public recall of all affected product and we have continued to push for this all along," the statement said.
Chinese officials have complained that they were only alerted last Monday of the dangers posed by the milk. They said Sanlu's customers had been complaining about the milk since March.
China's Health Minister, Gao Qiang, said on Saturday that Sanlu "should shoulder major responsibility for this".
He said those responsible for the contamination "would be dealt with severely". Nineteen arrests have so far been made over the scandal, Chinese authorities say.
Some of the tainted milk had been sent to Taiwan but none had been sold to other foreign markets, Mr Gao said.
Melamine has been used by Chinese suppliers of animal feed components to make them appear to have more protein.
It was linked to the formation of kidney stones and kidney failure in pets in the United States last year, leading to thousands of deaths and illnesses.
A fake milk powder scandal in 2004 killed at least 13 babies in China's eastern province of Anhui.
Investigators found that the milk given to these babies had no nutritional value, and the resulting scandal triggered widespread investigations into food safety.