The soldier is being investigated by police detectives assessing terror threats, a source says.

A soldier accused of threatening New Zealand's national security is being investigated by counter-terrorism agents.

The 27-year-old soldier, who co-founded a white nationalist group, was in December charged with the unauthorised access and sharing of information that could prejudice the security of New Zealand.

The man, who has name suppression, has been detained by the Defence Force and is on open arrest at Linton Military Camp while he awaits military trial. A date is yet to be set.

Stuff has now learnt that detectives working for a terror assessment outfit, the Combined Threat Assessment Group (CTAG), are investigating the soldier and are speaking with family and close associates.

GEORGE HEARD/STUFF The March 15 attack showed the terror risk white nationalism and far-right extremism pose.

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CTAG is a multi-agency group, led by the New Zealand Security Intelligence Service (NZSIS) in partnership with the Defence Force and Police, is responsible for assessing terrorism threats to New Zealand and its interests.

A source close to the soldier said that two police detectives describing themselves as working for CTAG have been interviewing family and friends in the past month.

"They wanted to know about his history and his association with the right-wing nut jobs and what we know about that," they said.

"And his trip to Russia, but they wouldn't tell us anything more than what has been already made public. The interview went for over an hour."

SCREENGRAB/STUFF White nationalist group the Dominion Movement was co-founded by a New Zealand soldier who stands accused of threatening national security

The soldier and his partner were due to fly out to Russia for Christmas, but the trip never eventuated due to his arrest.

"He had told people that he wanted to have a white Christmas. We wonder whether the trip had anything to do with right-wing stuff."

Those close to the soldier are concerned he may have links to international neo-Nazi groups, such as militant group The Base, which has been charged with committing hate crimes by the United States' Federal Bureau of Investigation (FBI) after a recent sting.

It has been revealed the group's leader, American Rinaldo Nazzaro, was operating out of Russia.

"We have questions about how his trip to Russia was paid for as well because we have learnt from various people that he had lost a lot of money — and we don't know who he was giving his money too," the source said.

Stuff has been provided with no evidence that indicates the soldier had made contact with overseas groups.

The soldier has held two positions during his five years with the Defence Force that gave him access to privileged information and weapons.

Both the NZSIS and police refused to respond to questions, instead referring queries about the investigation the Defence Force.

A Defence Force spokesman declined to respond to specific questions, citing the ongoing prosecution of the soldier.

Stuff has revealed the soldier's extensive involvement in far right groups, which appears to have continued after he was interviewed by police in the wake of March 15.

The soldier has been identified as a founder of the Dominion Movement, a white nationalist group that promoted the same far right ideology supported by the March 15 terror accused.

RICARDO B BRAZZIELL/AUSTIN AMERICAN-STATESMAN VIA AP Those close to the New Zealand soldier are concerned he has links to international neo-nazi groups like The Base. (FILE PHOTO)

The threat posed by the far right and white nationalism was made stark by the March 15 attack. An Australian man now faces trial for the murder of 51 Muslim worshippers at two mosques in Christchurch.

In the weeks after the attack, New Zealand's intelligence agencies were criticised for failing to recognise the threat of far right and white nationalism.

New Zealand's national terror level, determined by CTAG, has remained unchanged at medium — "a terrorist attack is assessed as feasible and could well occur" — since a month after the March attack.

According to the Defence Force manual, "Open arrest involves only such restraint as may be necessary to ensure a continued presence. A member of the Armed Forces under open arrest is to remain in uniform except when in his or her quarters. The member is to attend such parades or musters as may be required. The member is not to consume alcohol. He or she may perform his or her normal duties".