The soldier, whose name has been suppressed, admitted to attempted espionage, accessing a computer system for a dishonest purpose and knowingly possessing an objectionable publication.

He was ordered into military detention at Burnham Military Camp near Christchurch and will be dismissed from the New Zealand Defence Force at the end of his sentence.

His admission and its acceptance by the court marked the first spying conviction in New Zealand's history.

The soldier will be paid at half his previous rate until his dismissal at the end of his sentence, the defence force told AFP.

According to information provided to the court, he previously earned NZ$2,000 (US$1,600) a fortnight.

The court martial at Linton Military Camp near Palmerston North heard the soldier gave military base maps and photographs to an undercover officer posing as an agent for a foreign nation.

During the investigation, he was also found to have copies of a livestreamed video of the March 2019 killing of 51 worshippers at two mosques in Christchurch by white supremacist Brenton Tarrant.

- 'Harm to the world' -

The soldier became a person of interest after the Christchurch attack because he was a member of some right-wing groups that police were cracking down on, the court heard.

While monitoring him, the New Zealand government became aware he had "made contact with a third party, indicating that he was a soldier who was wanting to defect", according to an agreed summary of the facts read out by the prosecution.

The military court has permanently suppressed the identity of the foreign nation.

Chief Judge Kevin Riordan said the soldier "intended to prejudice the security and defence of New Zealand".

A military panel agreed the worst of his offences was the sharing of passwords, an identity card, and access codes to Linton Military Camp and the air force's Base Ohakea, the judge said.

"You were actively searching for things to supply to someone you thought was a foreign agent," Riordan said.

Of the man's video of the Christchurch killings, the judge said: "Keeping the message of a gross murderer is a harm to the world in itself."

The court martial was held in a large, cold hall at Linton, with banners carrying New Zealand Army slogans of "courage", "commitment", "comradeship" and "integrity".

"You have comprehensively breached all of these values," Riordan told the soldier.

The chief judge expressed concern over how the sentence would be perceived given that military detention is widely considered to be easier than civilian prison.

- 'No remorse' -

The military panel determined a starting point of between 3.5 and 4 years prison and gave deductions for the man's guilty plea and time spent under open arrest.

"We spent more time over this decision than any other," Riordan said.

The panel decided military detention was appropriate given the rehabilitation it would provide.

Crown lawyer Grant Burston had earlier told the court the soldier's sentence should start at between 4.5 and 5 years in prison.

"There is no apology," Burston said, referencing the soldier's affidavit, which was read to the court.

"There is just expressed regret and a well-established expression of grievance.

"There is no remorse for betraying... his country."

Defence lawyer Stephen Winter said that although the offences were serious, they were "at the bottom end of offending for this particular charge".

"He has grown out of that phase of his life. He is now a husband... a father," he said.

The soldier was arrested in December 2019 and had spent all but six days since then under what the New Zealand Defence Force called open arrest.

He was required to live on an army base in a military house and was subject to a curfew.

The soldier had been suspended on full pay, earning nearly US$204,000 (NZ$350,000) since his arrest.

During that time, he married and had two children. His wife is expecting a third child.

The New Zealand Defence Force declined to say whether his family would be provided housing during his detention.