The country's second-highest military commander has been temporarily relieved of his duties under mysterious circumstances, but officials at National Defence made clear on Monday Vice-Admiral Mark Norman has not been the subject of a criminal investigation by the Forces.

News leaked early in the day that Norman, who was appointed to the post of vice chief of defence staff last summer, was suspended but not stripped of his command.

A letter circulating among senior commanders of the military, dated Friday, says Norman was removed from his job "effective immediately" and will be replaced on an interim basis by the head of the navy, Vice-Admiral Ron Lloyd.

The country's top military commander, Gen. Jonathan Vance, ordered Norman to relinquish his responsibilities and offered no explanation.

Officials in Vance's office refused to provide further comment on the circumstances, but an official with the Canadian Forces National Investigative Service said the organization is aware of the order by the chief of defence staff.

"Military police are not investigating any matter regarding Admiral Norman at this time," said Lt. (navy) Blake Patterson, who added the service has also not been asked to assist in any outside law enforcement agency.

National Defence has refused to say whether any other kind of administrative investigation is underway.

A statement from Defence Minister Harjit Sajjan backed Vance, but also did not provide further explanation.

"I fully support the decision taken by the (chief of defence staff) to relieve the (vice chief of defence staff) from the performance of military duty," Sajjan said.

Under military law, an officer can be relieved of duties for administration or internal reasons related to discipline. The exceptional act can also occur in advance of the military trial.

Retired colonel Michel Drapeau, a legal expert, says he can't remember when someone so close to the top of the military was removed from their responsibilities under such a cloud.

"It is extremely unusual," he said.

Conservative defence critic James Bezan said the Forces and National Defence hadn't provided "any reason" as to why Norman was temporarily relieved of his duties.

"This situation is unprecedented and it is odd that the government and the military are not providing any details. Of course we expect all necessary precautions to be taken when there are national security and privacy implications involved," Bezan said.

"However, when a decision of this magnitude is made Canadians deserve to be kept informed."

Rare cases

There have been a handful of cases in recent years where senior overseas commanders have been ordered to step down because of allegations of inappropriate relationships.

In at least one case, the accusations were later found to be baseless.

The statement by military police effectively removes any suggestion Norman's suspension might be related to the ongoing campaign to stamp out sexual misconduct and abuse within the ranks.

That scandal has shaken National Defence to its core.

Some in the defence community, such as Drapeau, have been concerned about the seemingly arbitrary way senior brass have handled cases involving high-ranking officers.

The example often cited is the former commander of Canadian peacekeeping troops in Haiti, retired colonel Bernard Ouellette. He was stripped of his post after allegations were made of an "inappropriate relationship" with a United Nations staffer following the massive earthquake in 2010.

After being relieved Ouellette was the subject of two internal investigations, which cleared him. The Canadian Forces National Investigation Service concluded, at the time, there was "insufficient evidence to support the charge."

The military's internal grievance authority also said Ouellete was treated unfairly and "was not afforded procedural fairness."

The once-rising star within the military eventually sued the federal government, but the case was tossed out by the Federal Court.