Consumers warned as poison threat to New Zealand infant formula made public

New Zealand food safety officials are advising consumers to check infant formula packaging for tampering after an anonymous threat to poison the products.

Police revealed the threat on Tuesday four months after it was made to farming and dairy company leaders ahead of the perpetrator's warning that they would go public if their demands were not met.

Police said letters were sent to the Federated Farmers industry group and the Fonterra dairy cooperative in November last year.

They were accompanied by small packages of milk powder that subsequently tested positive for the presence of a concentrated form of the poison 1080.

The letters threatened to contaminate infant and other formula with 1080 unless New Zealand stopped using 1080 for pest control by the end of March 2015.

The letter writer threatened to disclose the threat publicly if the government did not meet this demand by this time.

The matter was referred to police and a full investigation Operation Concord, involving up to 36 staff at different times -- had been working unsuccessfully to identify those responsible.

"Whilst there is a possibility that this threat is a hoax, we must treat the threat seriously and a priority investigation is underway," Deputy Commissioner (National Operations) Mike Clement said in a statement.

Federated Farmers president William Rolleston said the letter was of extremely serious concern, but he was confident that New Zealand's regulatory authorities and processors had created " formidable barriers" to any such threat being carried out.

"It's evident that the security surrounding dairy processing in New Zealand is second to none and the tamper proofing of the product is also first class," Rolleston said in a statement.

Stock exchange company NZX suspended trading of securities of three major dairy companies, including Fonterra.

Fonterra chief executive Theo Spierings said the criminal threat targeted New Zealand and the entire dairy industry.

"We have taken immediate and decisive steps to give our customers and consumers added confidence, including increased testing and security measures," Spierings said in a statement.

Fonterra had worked with the Ministry for Primary Industries ( MPI), the country's food safety regulator, to establish a validated testing regime that was being used by the dairy industry for both raw milk and dairy products targeted by the threat, he said.

MPI deputy director-general Scott Gallacher said the government 's first priority was protecting the health and wellbeing of consumers.

"We are confident that New Zealand infant and other formula is just as safe today as it was before this threat was made. People should keep using it as they always have," Gallacher said in a statement.

"The ability for anybody to deliberately contaminate infant and other formula during manufacturing is extremely low. Regardless, we encourage people to be vigilant when buying infant and other formula. Our advice is always to check packaging for signs of tampering."

Manufacturers maintained high levels of security as a normal routine, but security and vigilance had been significantly increased since this threat was received, he said.

"The combined MPI and industry testing programs confirm there is no 1080 in infant and other formula. We have tested just over 40,000 raw milk and product samples and we have had no 1080 detections," he said.

Sodium monofluoroacetate, known as 1080, is a poison used as a pest control to protect New Zealand's native flora and fauna against introduced pests such as possums and ferrets.

Its use has been controversial over the years with opponents saying it also poisons native animals and contaminates the environment. Endi