The Calgary Zoo says two 27-year-old men snuck onto zoo grounds Monday morning and climbed over the public safety fence surrounding a tiger exhibit, where one man suffered serious arm injuries.

Zoo officials held a news conference on Monday to discuss the details of the bizarre incident which happened at about 1:00 a.m. local time.

Grahame Newton, the director of corporate services at the zoo, said the men first made "unauthorized access" to the property by climbing over its exterior fence, which stands nearly 2.5 metres high and has three strands of barbed wire at the top.

They next headed towards the tiger exhibit on the west side of the zoo where one of the men then climbed the one-metre-tall public safety fence surrounding the enclosure.

About two metres in from the public safety fence, a second interior fence -- 4.5-metres high and electrified along four separate wires at the top -- cages the tigers off from the outside world. It is designed to "keep the tigers inside their exhibit area," Newton said.

The exterior side of the second fence is where the injured man made contact with a two-year-old Siberian tiger named Vitali, Newton said. It is believed that the man had his arm pulled through the fence after it became hooked by the animal's claw.

"The second man reportedly went to the aid of his companion and they managed to get away from the tiger," he said.

One of the men then used a cellphone to contact a zoo security guard, who apparently did not know that they were at the park.

"As soon as the security officer received this call, she ran toward the tiger exhibit and encountered both men on a public path just east of the tiger enclosure," Newton said.

Security officers called 911 and started performing first aid on the man injured by the tiger. Paramedics arrived soon after and took the man to Foothills Hospital for treatment.

Newton also described the nature of the injuries that the man suffered.

"The information we have is that while his injuries appear not to be life-threatening, they are, however, quite serious," Newton said at the news conference.

The tiger was not injured as a result of the incident.

Calgary police are now investigating. The two men could potentially face charges.

Ted Trewella, the manager of zoo security, said four security officers were on duty at the time that the two men entered the park.

Newton said that the zoo is unclear of the intention of the two men who entered the park, though officials will be reviewing its procedures in the wake of Monday's incident.

"I think it's fair to say that if anybody puts their mind to it, they can breach any kind of security and that certainly seems to have been the case here," Newton said.

"An eight-foot (2.43-metre) fence with three strands of barbed wire in the top, it takes some effort to get over (the) top of that. And then, on top of that, to also scale another 42-inch (1.07- metre) fence and get inside that area between that fence and the tiger enclosure again requires some effort."

In an e-mail to CTV.ca, Calgary Zoo spokesperson Laurie Herron said three adult Siberian tigers -- two females and one male -- are kept at the zoo.

The Calgary Zoo website says Siberian tigers -- the kind of tigers present in the zoo's Eurasia exhibit -- typically grow to a length of 3 to 3.6 metres. Males can weigh between

180 and 306 kilograms, while females generally weigh between 100 and 167 kilograms.

With files from The Canadian Press