Wellington deployed troops on a "behind-the-wire" training mission in 2015 to boost the ability of the Iraqi Security Forces (ISF) to fight the Islamic State group.

Ardern said the small contingent of troops, currently 95, who have been working alongside the Australian army at the Taji military base north of Baghdad, had completed their mission.

"When it comes to Iraq, it's time to go," Ardern said, adding that 44,000 ISF personnel had been trained at the base.

"The New Zealand and Australian troops at Taji have worked hard, not only to provide training, but also to ensure that the ISF are well placed to take over this commitment at Taji in the near future."

She said New Zealand troop numbers at Taji would fall to 75 next month, then 45 in January 2020, before the withdrawal in June next year.

Defence Minister Ron Mark added that New Zealand would be reducing its troop numbers alongside their Australian counterparts.

Australia has yet to make a formal announcement on any downsizing of troop numbers in Iraq. The Australian defence department has been contacted for comment.