Former New Zealand prime minister Helen Clark on Wednesday denied sending non-combat troops to Iraq in 2003 to ensure one of her country's largest companies retained lucrative UN contracts.

A US diplomatic cable released by the WikiLeaks website this week reportedly cited New Zealand defence officials saying Clark opposed the Iraq deployment until she was told dairy giant Fonterra might lose UN "oil-for-food" contracts.

Clark, whose left-leaning Labour government was defeated in 2008 and who now heads the UN Development Programme, told Radio NZ she was "flabbergasted" at the "ridiculous" claim.

"I am absolutely incensed at the suggestion that some defence ministry personnel seem to have made to various diplomats that there was any connection between my support for sending engineers to do humanitarian work in Iraq with the interests of Fonterra," she said.

"I mean this is simply preposterous."

Two rotations of 61 New Zealand military engineers spent a year in Basra from September 2003 performing engineering and humanitarian tasks.

Clark said she always opposed the war in Iraq and would never allow commercial considerations to sway her decision-making on the issue.

She said the engineers were sent to Iraq in response to a UN Security Council request for help in reconstruction efforts following the US-led invasion.

Clark also defended the decision to keep secret a move to tighten military ties with the United States in 2007 following a rift dating back to the 1980s over New Zealand's anti-nuclear policy.

She said she did not want to create expectations in New Zealand that the country was resuming the full military alliance with the United States that was in place before the anti-nuclear row erupted.

The former prime minister supported her conservative successor John Key's choice to maintain the secrecy when New Zealand and Washington restored full intelligence ties last year without telling the public.

"There's always secrecy around intelligence relationship and I guess that's where I part company with the founder of WikiLeaks (Julian Assange) and others," she said.

"I actually believe that you do have to have areas of communication between governments and officials which aren't on the front pages of newspapers."

Questioned about WikiLeaks revelations that US Secretary of State Hillary Clinton asked US officials to spy on UN officials, Clark said the international organisation "takes a very a dim view" of such activities.

However, she was not concerned such snooping would reveal anything that was personally embarrassing to her.

"My life is an open book, it has been for so many years. If there's anything more they can find out, good luck to them," she said.