The Defence Minister is rejecting opposition calls for New Zealand troops to be withdrawn from their training mission in Iraq.

Labour and New Zealand First both insist that it's time the 143-strong contingent were brought home after the fall of Ramadi to the Islamic State, a major city not far from Camp Taji where NZDF personnel are based.

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US Secretary of Defense Ashton Carter was scathing after the defeat, saying the Iraqi Army - which Kiwi troops are supposed to be training - had no will to fight.

"What apparently happened was the Iraqi forces showed no will to fight," Carter said. "They were not outnumbered, and they vastly outnumbered the opposing force, and they failed to fight and withdrew from the site."

New Zealand First MP and former officer Ron Mark said one Kiwi solider's life isn't worth what they're doing in Iraq when $25 billion in training the military hasn't worked.

"You have ISIS [Islamic State], the best equipped terrorist force the world has ever seen now armed with a hundred and fifty-five millimetre artillery, now armed with Abrams tanks, now armed with T-72 tanks," he said.

"We shouldn't be there, should we?"

Defence Minister Gerry Brownlee disagrees, saying Mark's claims were "unreasonable".

"I think it's very unfortunate, I think it's unreasonable to subject the families of those soldiers who are there to this sort of political game-playing," Brownlee said.

"Should circumstances changes very dramatically then we've always said we'd be prepared to bring them home but the mission itself would be reviewed after a nine month period."