New Zealand police have begun interviewing people linked to an Auckland company over its association with the sale of 35 tonnes of North Korean explosives and anti-aircraft missiles to Iran.

Officers have spoken to a number of people with connections to SP Trading, a non-trading or "shell" company based in a multi-storey building in Queen St.

Their investigation was sparked after Thai police seized a cargo plane on December 12 that had been chartered by SP Trading. When the police boarded the aircraft they discovered explosives, rocket-propelled grenades and anti-aircraft missiles.

Police spokesman Grant Ogilvie yesterday told the Weekend Herald that police were assisting a number of government agencies to determine the links with any New Zealand formed company and the munitions seizure.

Of particular interest is SP Trading. A number of people with a connection to the company have been spoken to and the New Zealand police liaison officer in Bangkok is in close contact with Thai police.

"Any requests for assistance from Thai police will be dealt with as a priority by New Zealand police," Mr Ogilvie said.

United States authorities are also investigating because North Korea is banned from exporting any weapons. If it is proven SP Trading knew the weapons were going to Iran it could be indicted by the US Justice Department.

A spokeswoman said yesterday she knew of the matter but the department would not be commenting or confirm if indictment was imminent. The Ministry of Foreign Affairs and Trade said its inquiries were ongoing.

The Companies Office lists SP Trading Ltd's director as Lu Zhang. The company was registered last July. Its sole shareholder is Vicam (Auckland) Ltd, and that company's shareholder is GT Group Ltd. All three are registered to the Queen St address.

No one was at the offices yesterday.

HOW THE STORY UNFOLDED
* A Georgia-registered cargo plane stops to refuel at Bangkok's Don Muang Airport on December 12, 2009. It is found to have 35 tonnes of North Korean weapons onboard and is said to be heading to Iran. Five crew members, from Kazakhstan and Belarus, are arrested but deny any knowledge of the weapons.
* The plane has recently been registered by Queen St-based SP Trading which in turn is owned by GT Group Ltd. New Zealand authorities - police, Ministry of Foreign Affairs and the Serious Fraud Office - begin to investigate the New Zealand link to the horde of weapons.
* Police yesterday confirmed they have spoken to a number of people connected to SP Trading and will make it a priority if asked for assistance by Thai police. The US Department of Justice has confirmed it is aware of the incident but won't comment on if it will indict SP Trading or not.