The United States Embassy has apologised for releasing the sensitive cyanide letter that makes a terror threat to the America's Cup.
Police yesterday asked embassy staff in Wellington to explain how the letter was given to the CNN television network on Tuesday despite their requirements that it bekept confidential.
Police say its release compromised their investigation because few besides the author of the letter would have known the contents.
Embassy spokeswoman Janine Burns told the Herald last night that the letter had been released inadvertently and the US mission regretted the incident.
"It was a mistake. We have conferred with Washington to help ensure that this sort of thing doesn't happen again."
Identical letters were sent to the US Ambassador, the Australian and British High Commissioners and the Herald containing white powder.
The powder in the letter to the British High Commissioner has been confirmed as cyanide.
The letters were from a group called September 11, which said it has stockpiled 25kg of the deadly poison.
The police counter-terrorism chief, Assistant Commissioner Jon White, said CNN had told officers the letter's text was taken from a website and had been posted by the US State Department's Overseas Security Advisory Council.
The council is set up to share security-related information between the US Government and American firms working abroad.
The information had been provided through the American embassy, and Mr White said he met officials yesterday afternoon to discuss the leak.
The police had wanted to keep the letter out of the public domain for fear it might spark false admissions, "which we do get from time to time with these sorts of things".
Since releasing the letter police had received 70 calls to a hotline, 0800 THREAT or 0800 847-328.
