US Secretary of Defense Ash Carter has thanked the New Zealand Government for agreeing to extend its deployment to Iraq and the New Zealand public for what he described as its "staunch support" of the fight against Islamic State.

Prime Minister John Key announced yesterday he was extending the initial 2-year deployment of 143 troops to Taji Military Camp for a further 18 months and the trainers in Taji would also train security forces responsible for holding the territory won back from Islamic State, such as Iraq's military Police.

The decision followed requests from Secretary Carter for all the countries involved with the coalition to do more.

In a statement, Secretary Carter said he had discussed the matter with Defence Minister Gerry Brownlee at a meeting of the anti-Isil coalition members in Stuttgart last month, saying it had to be a global undertaking because ISIL was a global threat.


"Expanding the resources dedicated to the fight allows the coalition to further accelerate the campaign. I am grateful to the Government of New Zealand and Minister Brownlee for the decision to take these meaningful actions and to the people of New Zealand for their staunch support in this fight."

The decision to extend the deployment has been opposed by Labour leader Andrew Little who said he would withdraw the troops if he was Prime Minister after the 2017 election.

Mr Key's decision is contrary to his earlier statements that he did not want to stay for more than two years.

Mr Key said the continued deployment was contingent on four factors - including Australia remaining involved in the training mission and the security situation in Iraq.

The Government would consider withdrawing the troops if there was a significant deterioration in safety.