Labour leader Andrew Little told Australian Prime Minister Tony Abbott in their private meeting that Australia's air strikes against Isis in Iraq make sense because the Iraqis were saying air strikes were making a difference.
But he also told Mr Abbott that the plan for New Zealand and Australia to train Iraqi troops was an exercise in futility because it would be "propping up a corrupt and dysfunctional army".
Mr Little also told Mr Abbott that the description of sending New Zealand and Australian troops in a training mission "under some sort of Anzac tradition" was a sensitive issue in New Zealand and that New Zealanders did not necessarily see it in those terms.
Mr Little said dealing with Isis was more complex than "just knocking over the evil-doers".
"You can't negotiate with them but you have to cut off their funding supply, weapon supply, change the conditions in which they are recruiting young Muslims."
Mr Little spent 35 minutes with Mr Abbott at Eden Park - during which time Australia lost four wickets.
He took deputy leader Annette King with him because she had worked closely with Mr Abbott when both were health ministers.
Last week, Prime Minister John Key called on Mr Little to "get some guts" and to join the right side.
Labour oppositions in Australia, Canada and Britain support their Government's military involvement in Iraq.
Mr Key last week announced that New Zealand would join the coalition, with 143 Defence Force personnel to be deployed to the Middle East, 106 of them to Camp Taji just north of Baghdad for a two-year deployment.
Most would take part in training but there would be 16 specialist trainers, as well as protection and logistics personnel.
Australia has 600 Defence Force personnel there, mainly an air force mission which has conducted more than 500 sorties against Isis (Islamic State) and 200 Special Forces.
Mr Abbott is due to announce an expansion of 200 to 300 troops to work alongside New Zealand at Camp Taji.
Mr Little yesterday said a stable Middle East was in New Zealand's interests but it was not going to be achieved with 16 trainers and 120 logistics and security personnel for two years. "It's too small to make a difference."
Mr Key said yesterday that the same parties who say New Zealand won't make a difference in Iraq were the same ones that said New Zealand should make a stand against climate change "and when I say we're only 0.14 per cent of world emissions, they say it doesn't matter that we're small".