UPDATED 8.11am The Prime Minister's being called on to hold a formal inquiry into the SAS and its actions in Afghanistan.

LISTEN ABOVE: Hit and Run Co-author Jon Stephenson spoke to Rachel Smalley

Authors Jon Stephenson and Nicky Hager are seeking the move, alleging in their new book Hit and Run that the SAS killed and wounded civilians during a raid in 2010 and that the military then covered the fact up from the public.

They claim the operation was in retaliation to the killing of New Zealand soldier Lieutenant Tim O'Donnell, and could have involved war crimes.

LISTEN: Nicky Hager speaks with Mike Hosking

Co-author Jon Stephenson told Rachel Smalley they know the Apache helicopter team didn't discriminate its targets well enough during the raid.

"But we don't know what happened on the morning in terms of what the ground commander said, where the helicopter should be and what they should open fire on, and if he gave them any orders to cease the firing."

Mr Stephenson said an inquiry could clear up these questions... but the Defence Force has ruled it out.

SEE ALSO: Rachel Smalley: Did the Defence Force commit a war crime?

Defence Minister Gerry Brownlee is overseas, but via a spokesperson acting Defence Minister Chris Finlayson said the matter was investigated at the time and he's been advised by the New Zealand Defence Force they stand by what they said at the time.

Mr Hager is looking forward to the government's response, and said he is more optimistic about getting an inquiry from Bill English than he would have been from John Key.

"Bill English might take a more reasonable approach to this, rather than just making excuses or calling us names" he said.

Mr Stephenson said Mr English is an honourable person and a decent man.

"Bill English is the sort of guy, if he's presented with the honest information from the military, that he will do the right thing."

LISTEN: 'I think you could make a pretty strong case these constituted war crimes' 

Mr Hager believes former Prime Minister John Key would have heard details about the attack and its consequences and he's at a loss to know why Mr Key didn't want it investigated.

"And that's where I feel he's most culpable is that he, having made a decision, which he presumably thought was right, he did nothing later when it was evident that it had gone wrong, or there was strong suggestion that it had gone wrong.

And being relaxed and comfortable at that stage is not what you need from a leader."

Meanwhile, Mr Key is making it clear sending soldiers into harm's way was something he took very seriously when he held the top office.

In an interview given yesterday, before the book was made public, he made it clear some of the most challenging times he had as Prime Minister was when we lost military people overseas.

"I think when you're Prime Minister and you send people to Afghanistan or Iraq, or whatever it might be, you have to do that with your eyes open, that there's a chance that you'll lose people on your watch, and I always took that very seriously and personally."

The Prime Minister's Office is saying little, other than they've not read the book.

And Mr Key, who was Prime Minister when the operation was approved, has referred queries to Bill English's office.

In a statement, the Defence Force said it stands by the actions of New Zealand personnel, and won't investigate the actions of other soldiers.

It said a joint Afghani and International Security Assistance Force investigation found allegations of civilian deaths were unfounded.