Nevertheless, there was the prospect that Iraqi troops could turn on their New Zealand and Australian trainers.
"That is without doubt a risk", Mr Key said.
"It was a risk that materialised into tragic deaths in Afghanistan and it's something that we'd have to be vigilant about. I can't say to New Zealanders that there's no risk if we send our trainers there, there definitely is, but it's far less risky, I would suggest, than if they were on the front line."
He said there were techniques to reduce that risk including limiting access to weapons on the base and thorough vetting of Iraqi personnel.
This morning he acknowledged that if New Zealand did work with Australia, our troops could serve under Australian commanders.
"All of those issues would need to be worked out, but in principal we would obviously have to have, if not joint command, very senior leadership. I would have thought it would be joint but we'd have to work our way through it."
Addressing suggestions an Anzac-badged unit Iraq was not appropriate given the history of the name, Mr Key said: "We wouldn't want to do something that was disrespectful".
"I think there would also be a lot of people who would say Australia and New Zealand working collaboratively together in a range of different fields makes sense. Maybe having a badged unit is something that demonstrates the solidarity between Australia and New Zealand."
Defence Minister Gerry Brownlee yesterday confirmed defence personnel had begun training for potential deployment to Iraq.
The Herald understands they include members of the Royal New Zealand Infantry Regiment 1st Battalion's Alpha Company, based at Linton near Palmerston North, as well as engineers and training personnel.
Mr Brownlee said through a spokesman that the Defence Force had begun "some training and preparation on a contingency basis".
"This is required to ensure there is a suitable time to build an effective level of capability should the Government decide to deploy."
Training will focus on areas that cannot be developed to a sufficient level of competence in a short time-frame, such as language and cultural training, and risk mitigation measures. The units involved are those whose capabilities are most likely to be called upon in that environment, should an NZDF deployment take place."