New details of a cyanide threat against a New Zealand golf tournament starring Tiger Woods have been revealed.

Labour MP Trevor Mallard was duty minister when a cyanide-laced letter was delivered to the United States Embassy in Wellington.

The letter, delivered in December 2001, threatened terrorist action against the New Zealand Golf Open, due to take place the following month with Woods attending.

Mr Mallard, who recalled the subsequent security operation after this week's reaction to the 1080 milk formula threat, said it was believed to be a hoax but still taken seriously.

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Police tightened security at the golf open at Paraparaumu, north of Wellington, and warned the public to be vigilant against food and drink tampering, but were not more specific.

Mr Mallard told the Herald that the cyanide sent to the US Embassy was contained in sealed sugar sachets.

"It resulted in a pretty major alert. Much heavier both plain and uniformed police presence, and significant army presence at the golf but also on routes to the golf. It's different to the current one [1080 contamination threat], because the threat was more limited. It was limited to an event, and there was very close monitoring of the particular product [sugar] at the event."

Police later confirmed that enough cyanide was sent to the embassy to kill several people. Woods' management team were informed of the letter.

NZ police today revealed that letters threatening to poison milk formula powder with 1080 have been received.

The cyanide letter's author was not identified or caught. Its sending was later believed to be linked to more cyanide threat letters.

A group calling itself September 11 and claiming to possess 25kg of cyanide sent letters to the US Embassy and the British and Australian high commissions threatening an attack on the 2003 America's Cup in Auckland. The threats led police and health chiefs to make a rare public warning for all Kiwis to be vigilant when taking public transport, eating in restaurants or in public, and eating packaged foods.

Other letters referencing a cyanide attack were sent to the Herald in the same year.