New Zealand elite soldiers killed six civilians and injured 15 during a raid in Afghanistan in 2010, author Nicky Hager's new book alleges.
Hager is launching his latest book Hit & Run at an event in Wellington.
Hundreds of people have crammed into the Unity Books store, including a large media contingent.
Hit & Run, which was co-authored with freelance journalist Jon Stephenson, is based on the NZ Special Air Service's (SAS) response to the first New Zealand death in combat in the country.
Soldiers involved in the raid approached the two authors and said they believed they had been involved in war crimes, Hager said at the book launch today.
New Zealand's Defence Minister at the time of the raid, Wayne Mapp, has previously said that no civilians were killed.
Speaking to media after the book launch, Hager said he and Stephenson had discussed the raid with legal experts and they had said there were grounds to suspect war crimes had been committed.
"That is a very serious allegation and it has to be determined by experts, which is why we are calling for an inquiry."
Both Hager and Stephenson said they believed some of their sources would be willing to front an inquiry if it were established.
Hager said the raid was more than incompetence, but he was not alleging soldiers had planned to kill civilians.
It was still unclear how much then Prime Minister John Key and others were told after the raid.
"There are two possibilities - one is the Government has been misleading the public, the other is that the Government has not been told the truth by the military."
Hager said both he and Stephenson had been approached by people in the military.
"The insiders that we talked to were not happy people."
Hager said their sources "were there at the time".
"This is coming from the horses' mouths completely."
Stephenson said Prime Minister Bill English would not ignore the raid and its aftermath.
"I think Bill English is an honorable guy. You may disagree with his politics but he is a decent man. I think we would appeal to him as a son, as a father, as someone who understands what it might be like to lose kids, that he will reach out and do the right thing here. Because this is a wrong that has...festered for years."
Hager said the sources believed NZ's SAS had been involved in war crimes.
Hager said an SAS group had led a raid that came after then PM John Key's approval.
None of the suspected fighters were in the targeted villages, but families and children were.
Six people were killed, including a young school teacher, Hager said, and a young girl.
The SAS destroyed about 12 homes in the village, he said.
Since the raid there had been a cover-up, he said, including claims only insurgents had been killed.
Hager said the Government needed to establish an official inquiry, and apologise to villagers affected.
Lastly, he called for a restructure of the SAS.
Stephenson said the book was not anti-military. It could not have been produced without sources within the military.
"We cannot name them but they know who they are."
There had been speculation that the topic was Afghanistan, and in an interview with Fairfax earlier today, former Prime Minister John Key said he was comfortable with decisions made during the Afghanistan deployment.
"I am absolutely confident that we took very clear, legally sound and appropriate advice. I don't have any doubts that our people did what they had a mandate to do - and that they did the right thing."
He said it was a "logical" place for Hager to look at, describing him as "a massive left-wing conspiracy theorist. The man sees shadows."
The launch had been shrouded in secrecy - even the book title had been kept secret.
But Hager's books have a habit of stirring political controversy.
His 2014 book Dirty Politics showed how the National Party collaborated with right-wing bloggers to attack its opponents and critics, which led to a police raid on Hager's home.
Dirty Politics was released a month before the election and the allegations of dirty tricks by former Prime Minister John Key's office dominated much of the election campaign, though National's popularity was not dented and it eased to a third term in Government.
Hager also wrote the The Hollow Men, which used leaked emails to reveal details about National's election strategy in the 2005 election campaign, and Seeds of Mistrust, which covered the alleged cover-up of a genetically-modified crop release in New Zealand.