In August, Sanlu's testing "revealed melamine in the baby milk powder and showed that it was contaminated," the ministry statement said. It did not say when Sanlu alerted authorities about its findings. On Thursday, the dairy announced a recall of 700 tons of formula made before Aug. 6.

A New Zealand dairy cooperative that owns part of Sanlu said Friday it believed none of the tainted powder was exported.

Kidney problems in infants were reported as early as mid-July but authorities failed to launch a food safety investigation, the official Xinhua News Agency said. Another news report said the dairy received complaints as early as March.

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