Kidney stones and renal failure has been reported in children in China, where three have died and a further 13,000 hospitalized, believed to be associated with the ingestion of melamine-contaminated infant formula.

Melamine was deliberately added to raw milk for several months to boost its apparent protein content, WHO said.

Commonly used in such materials as containers and labels, melamine can also be found in agricultural products such as fertilizer. Alone, it is of low toxicity, but animal studies have suggested that kidney problems occur when combined with cyanuric acid.

The new WHO guidelines – “Melamine and Cyanuric acid: Toxicity, Preliminary Risk Assessment and Guidance on Levels in Food” – seek to help national authorities assess the risks of melamine levels in food.

But the agency cautioned that this is only a preliminary assessment with more data needed, adding that it is currently working towards a more thorough assessment through meetings with scientists from around the world.

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UN agencies call for vigilance on contaminated milk products