Prime Minister John Key has ruled out sending the SAS to join New Zealand’s contribution to the fight against ISIS.

It follows a request from United States Secretary of Defence Ash Carter last year.

Mr Carter sent a letter to all countries already participating in the fight in Iraq and Syria asking them to increase their contribution and consider sending special forces.

Australia and the United States have deployed special forces.

However, John Key said New Zealand won't be following suit, because that doesn't fit in with the commitment the Government wants to make.

LISTEN ABOVE: Strategic Analyst Paul Buchanan speaks to Larry Williams

Strategic analyst Paul Buchanan said it's unusual for New Zealand to reject a direct US request.

"A request that has been accepted by many other allies, including the Canadians, Norwegians, the Danes, even the Poles are putting special operators in."

He said if New Zealand wants to play a leading role in the international community, it should play a more active role in the fight against ISIS.

"Leaving them in the barracks in Papakura is somewhat a kin to leaving a Bugatti in a garage. These guys are elite troops, they're ready to go, they're volunteers."

Buchanan said it's particularly bizarre since New Zealand already appears to have SAS troops stationed in Iraq.