Canada's newly armed border guards have claimed their first victim: a hapless moose.

The creature was felled by the duty sidearm of a border officer in late August, newly disclosed documents show.

The incident - marking the first time a border-guard sidearm has been discharged on duty - occurred about 25 kilometres west of Creston, B.C., as an unidentified intelligence officer with the Canada Border Services Agency was driving on official business to Nelson, B.C.

The officer was behind an RCMP vehicle when both drivers spotted an injured moose struggling in the westbound lane of Highway 3.

The animal had suffered serious injuries to the rear legs and pelvis, and was crawling forward into the eastbound lane using its front legs.

The RCMP constable decided to put the moose out of its misery and prevent a possible highway accident, say documents obtained by The Canadian Press under the Access to Information Act.

The constable discharged his pistol twice into the moose's head, which brought the animal to a stop but did not kill it.

The Mountie "then requested that (the) CBSA intelligence officer ... euthanize the moose based on his known familiarity with livestock," says an official report into the incident.

The border services officer "discharged one round from his CBSA duty pistol into the head of the moose, resulting in the death of the animal."

The carcass was then removed from the flow of traffic.

An internal review of the Aug. 26 incident, required whenever a sidearm is even drawn, absolved the officer of any wrongdoing, noting that he was requested by a police officer to assist and that the injured moose was a serious threat to traffic.

"The drawing, pointing and discharge of the duty firearm by officer ... was justified," the review concluded.

A spokeswoman said all procedures worked as intended.

"As in all cases in which CBSA officers use their defensive tools, agency officials thoroughly reviewed the incident," Patrizia Giolti said in an email.

"CBSA operational procedures are developed and designed to ensure the safety of the public and of CBSA officers."

Canada's border guards began to carry sidearms in July 2007, and are pulling them from their holsters about three times a month. The moose incident is the first time there has been a discharge.

As of March this year, more than 800 border officers had been trained and assigned a duty firearm, the 9 mm Beretta P4X Storm.

The agency wants to arm 4,800 guards at all land and marine border points by 2016.

Agency officers are stationed at more than 1,200 locations across Canada, including 14 international airports and 119 land crossings.