He also said that there was no pressure from New Zealand's American allies to join the Middle East conflict.
"I can't recall a conversation I've ever had with the Americans. They've certainly never asked me, I don't think they've asked our system."
New Zealand's primary reason for considering a deployment was because the Islamic State's activities were "utterly reprehensible".
"The decision ... we make next week ... is a decision based on New Zealand's view that we've got to be part of standing up against Isil," Mr Key said.
"It's not a matter of just waving our flag, it's a matter of stopping Isil and forcing them back."
Labour is concerned about a deployment to Iraq, questioning whether New Zealand will get caught up in endless, messy conflict.
Mr Little said Dr al-Jaafari had made it clear that troops on the ground were not a priority, and American airstrikes had proven successful so far.
The Labour leader said he supported the airstrikes, and he also supported the use of New Zealand spy agencies to identify targets.
Cabinet will decide next week whether New Zealand will make a deployment to the Middle East.
There was confusion after last week's talks about whether New Zealand's trainers would be protected by New Zealand or Iraqi forces.
Mr Key confirmed that New Zealand troops would protect the trainers "behind the wire" but there might also be further protection from Iraqi troops and other nationalities.
A New Zealand deployment would likely number 100 people, a large proportion of which would be force protection.
Mr Key said he could not rule out New Zealand troops going outside the base to engage in a firefight because he had not been briefed yet.
He was confident Government could resolve questions about whether New Zealand troops would be able to defend their trainers.
"Obviously we wouldn't send our people unless we're confident that they can undertake whatever actions are required."
Asked whether he wanted them to have the power to shoot and kill in self-defence, he said: "We have to make sure people have the correct legal authority to do their activities."
Defence Minister Gerry Brownlee said one of the bases being considered for a New Zealand deployment was Camp Taji, around 30km from Baghdad.