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America's top policeman was at the head of an international security summit held under extraordinary secrecy in Queenstown.

The summit's cover was blown only when United States Federal Bureau of Investigations director Robert S. Mueller III was seen boarding an unmarked Gulfstream 5 jet for Australia yesterday at Queenstown Airport.

The Prime Minister refused to comment on the summit, but a Government official last night confirmed Mr Mueller had been in Queenstown as part of a conference of English-speaking security chiefs.

Police diplomatic protection squad members had joined his security screen.

As the US mourned its dead on the six-month anniversary of the September 11 terrorism attacks, Mr Mueller was heading for a series of meetings understood to include a special briefing of Australian Prime Minister John Howard.

Mr Mueller, who had been in office for only a week when the terrorists struck, flew to Canberra just before 1pm after three days in New Zealand.

Another Gulfstream 5, with US Air Force markings, left before him.

The FBI director was one of about 20 guests, including security chiefs understood to be from the US, Britain and Australia, who stayed at Millbrook Resort near Arrowtown.

Mr Mueller, a former US Assistant Attorney-General, heads a crime-fighting agency of almost 30,000 employees, of whom more than 7000 are investigating the September 11 attacks and sequels such as the anthrax mailouts.

The guests and about 30 minders, who are also understood to have included an US hostage rescue team in case of a terrorist attack, had two dinners at Queenstown restaurants outside Millbrook.

Camera-toting tourists were politely bailed up and briefly interrogated by special agents around Millbrook. Reporters and photographers were told that a group of "overseas officials" were holding low-level talks.

New Zealand diplomatic protection police and US Secret Intelligence Service agents wearing International Affairs Forum badges vetted visitors entering or leaving the resort.

Gibbston Valley Winery general manager Ross McKay said agents clearing the way for a dinner at his restaurant on Sunday night were as thorough as for former US President Bill Clinton's visit in 1999.

"They looked in the fermentation vats and had a good look at a mobile bottling plant," he said.

Helen Clark's chief press secretary, Mike Munro, said he had been told not to discuss the conference.

Detective Superintendent Bill Bishop, the police national crime manager, said of the Queenstown operation: "We haven't got anything to say in respect of any activity that occurred down that way."

Wellington international affairs commentator Terence O'Brien, a former New Zealand ambassador to the United Nations, challenged the Government last night to "come clean" and tell the public what was happening in Queenstown.

"Having foreign police forces on your soil is an issue for national consideration - we are not a national security state."

Mr O'Brien said that if the head of the FBI was making a tour of New Zealand and Australia, it disclosed a new international role for what was traditionally a domestic criminal investigation force.

The FBI's headquarters in Washington DC would not comment last night on Mr Mueller's visit, but invited the Herald to call back today.