New Zealand investigating threat to poison baby formula; Fonterra sent poisoned milk packets

New Zealand police are investigating an anonymous threat to poison infant formula as part of a protest over the country's use of poisonous baits for pest control.

Prime Minister John Key said on Tuesday that the threat was likely a hoax, and assured parents that formula was safe for babies to drink. But the announcement prompted fears of a backlash against the country's economically crucial dairy industry.

Police say dairy giant Fonterra and farming association Federated Farmers both received anonymous, threatening letters in November. The letters were accompanied by small packages of milk powder that tested positive for a concentrated form of the agricultural pesticide 1080.

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