Two other firms to be closed down were connected to the sale of tainted pet food in the US which caused the deaths of hundreds of cats and dogs.

 

The General Administration for Quality Supervision, Inspection and Quarantine said the companies had "unlawfully added melamine" to some of their products.

 

Used in plastics, fertilizers and flame retardants, Melamine has no nutritional value but is high in nitrogen, making products appear to be higher in protein.

 

Announcing the decision to suspend the firms licenses, the safety watchdog also said it was taking legal action against the firms' managers.

 

China has attempted in recent weeks to clean up its tainted food and drugs industry.

 

Besides cracking down on errant firms, it has executed the former chief of its food and drug safety watchdog for corruption, lashed out at the media for exaggerating reports and banned imports from other countries to show it was not the only country that exported questionable products.

 

WHO support

 

On Thursday, state-run media ran prominent reports quoting the head of the World Health Organisation (WHO) saying that China should not be singled out for poor food safety.

 

Margaret Chan, the WHO director-general and a Hong Kong native, said food safety was a big problem in both developed and developing countries and all nations should strengthen their regulatory frameworks.

 

China also warned the US on Thursday against "groundless smear attacks" on its products, saying it was working responsibly to address concerns.

 

"The Chinese government has not turned a blind eye or tried to cover up. We have taken this matter very seriously, acted responsibly and immediately adopted forceful measures," a statement from the Chinese embassy in Washington said.

 

"Blowing up, complicating or politicising a problem are irresponsible actions and do not help in its solution.

 

"It is even more unacceptable for some to launch groundless smear attacks on China at the excuse of food and drug safety problems," it said.