The World Health Organization said Friday the scandal over milk products contaminated with the chemical melamine was worsened by “ignorance and deliberate failure to report” problems by local authorities.

"We understand that this incident was aggravated by delays in reporting at a number of sources," Hans Troedsson, the WHO representative in China, told reporters.

"These delays were probably a combination of ignorance and deliberate failure to report," Troedsson said.

"If information had been reported as soon it was learned, we would not have seen an incident of this scale," he said.

At least four infants have died as a result of consuming melamine-contaminated milk powder, while some 13,000 infants were hospitalized and 40,000 others experienced health problems, according to the health ministry and state media.

Jorgen Schlundt, WHO's director of food safety, said the poisoning showed the importance of breastfeeding for babies.

"But it is also critical to ensure that there is an adequate supply of safe infant formula to meet the needs of infants who are not breastfed," Schlundt said.

"This outbreak was caused by the intentional addition of high concentrations of melamine to milk," he said.

Troedsson said WHO experts were working with Chinese officials to develop a new food safety monitoring system with a strong regulatory framework and proper enforcement, and has recommended the setting up of a consumer protection system.

Part of the problem in China was the weak supervision split between up to 16 different authorities, and China needed to develop a "culture of openness and quick reporting" in the food industry, Schlundt said.

"Clearly change needs to happen so that you get a system that is really coherent and you have very quick reporting whenever you have public health threats," he said.

But Troedsson said the central government appeared to have acted quickly and appropriately once it was informed about the problems of melamine contamination.

"That reporting at the national level has, I think, worked well," he said.

After initial complaints about milk powder, health inspectors later found melamine in some liquid milk and yoghurt sold by three leading dairy producers.

On Friday, the producers of White Rabbit candy, one of China's best-known confectionery brands, suspended sales over suspected melamine contamination.

The White Rabbit brand is owned by the Shanghai-based Bright Dairy company, some of whose liquid milk and yoghurt had already been found to contain melamine, the official Xinhua news agency said.

Melamine is used as a binding agent and coating for particle, fibre and laminated board in furniture. It is also used to make fertilizer.