Prime Minister John Key has attacked the credibility of the journalist who has raised questions about New Zealand's elite soldiers in Afghanistan and whether they were complicit in torture.

And the Defence Force has released unprecedented details about SAS operations in a bid to discredit an article in this month's Metro, written by journalist Jon Stephenson.

The article outlined two instances last year where SAS forces allegedly captured suspects and handed them to Afghanistan authorities, including the Afghan secret police, the National Directorate of Security, which has a reputation for torturing prisoners.

New Zealand has signed several international conventions outlawing the inhumane detention of prisoners, including torture.

Stephenson last night countered by challenging the Defence Force to face an independent inquiry. "I'm happy to put my information before an inquiry. Any fair or impartial inquiry will show that they are the ones misleading the public. Not me."

Mr Key said the assertions outlined in Metro did not stack up under the NZDF microscope.

"I've got no reason for NZDF to be lying, and I've found [Stephenson] myself personally not to be credible," Mr Key said.

"Jon Stephenson's a guy that texted me one night impersonating [TV3 political editor] Duncan Garner ... I hung up on him, because when people impersonate somebody else, I don't take them seriously."

Stephenson said he sent the text two years ago believing the recipient to be Garner. He was surprised when Mr Key called him, but he identified himself immediately and the two had a brief, friendly conversation.

Earlier, Defence Force chief Lieutenant General Rhys Jones said incidents outlined in Metro were either inaccurate or did not happen.

The SAS did not detain anyone in an operation last Christmas Eve, and had never intervened when Afghan authorities were about to tie a prisoner to a vehicle and drag him.

General Jones also said a commander at the Crisis Response Unit, quoted in Metro, told the NZDF that he had never spoken to Stephenson.

He said the SAS had a reputation in Afghanistan for their "assiduous attention" to human rights, and followed processes that were legally and morally sound.

Stephenson said General Jones was playing "legal gymnastics".

There were no detainees in the incident last Christmas Eve in the sense that no suspects were taken to prison, he said, but he reported that the SAS had detained people by holding them at gunpoint and forcing them to their knees as they searched the building.

Stephenson also said the source of his story about the SAS intervention was credible. His translator could confirm the interview took place, he said.

"I go to great lengths to ensure that my reporting is accurate, fair, and I regard [this] as an unjustifiable attack on my credibility."