The RCMP's national terrorism unit is investigating a second explosion on a gas pipeline in northern B.C. near Dawson Creek, causing some to fear more attacks are on their way.

The force says it appears both explosion are linked, and there was a threatening letter sent to local media.

RCMP Sgt. Tim Shields told CTV Newsnet on Thursday afternoon that the explosion targeted a natural gas pipeline owned by EnCana.

He told earlier on Thursday that a specialized unit had been called in to investigate the first bombing. The unit will now investigate both incidents.

Shields said the Integrated National Security Enforcement Team (INSET) is helping investigators determine who was behind the incidents.

He said it appears to be a "deliberate act" that left a crater below the pipeline. But he noted the pipeline did not rupture, although it was damaged.

"There was a small leak in the pipeline that was contained and there is a hole in the ground," Shields told Newsnet.

Pipeline workers discovered the latest explosion site off Highway 2, about half a kilometre from the B.C.-Alberta border. It appears to be related to another pipeline blast in the area earlier this month, Shields said.

Police in Dawson Creek said someone planted the initial explosive device over the weekend near a sour gas pipeline operated by EnCana.

That blast left a 2.5-metre-wide and 2-metre-deep crater in the ground. It dented the pipeline, which didn't rupture. Otherwise, police said the explosion could have been much worse, noting that sour gas is toxic.

An ominous letter

According to the RCMP website, "INSET members are better able to track, deter, disrupt and prevent criminal activities (major or minor offences) of terrorist groups or individuals who pose a threat to Canada's national security."

Shields told on Thursday -- before details of the second blast became public -- that the unit has been "investigating since day one because it was a direct attack on the infrastructure of British Columbia and that's part of their mandate."

At the time, Shields said the initial investigation was not a terrorism probe, but instead police were treating the incident like an "isolated criminal act."

"There appears to be an agenda involved, but we're not characterizing this as an act of terrorism," he told by phone from Vancouver on Thursday morning.

He said police had warned gas and oil companies in the area before the first incident about a suspicious letter that was sent to local media outlets on Oct. 10. It told the companies to cease production and leave the area, but did not contain a specific threat.

"We will no longer negotiate with terrorists which you are as you keep endangering our families with crazy expansion of deadly gas wells in our home lands," said the anonymous letter, parts of which were published by the Dawson Creek Daily News, according to The Canadian Press.

Shields said investigators are curious about the timing of the letter, which came just a few days before the first blast on Oct. 12 bombing.

After the second blast, Shields said the letter and explosions appeared to be linked.

Terrorism expert John Thompson said it appears the bombing aren't the work of organized environmental groups.

"This also suggests that this is a small, amateurish effort by community activists," Thompson, president of the Toronto-based Mackenzie Institute, told The Canadian Press

"It's either somebody who is particularly torqued off by the oil and gas industry specifically, or someone who is self-actualized as a radical environmentalist with their own strange ideas about how to fight."

EnCana spokesman Alan Boras told CP before the discovery of the second incident that the company's facilities in northern B.C. haven't been targeted before. He also said the company has good relations with community members.

"It doesn't mean we don't from time to time have concerns. We work very hard to work through them," Boras said.

One area resident also told CP that some landowners have been fighting for more land use rights.

Gwen Johanson, a representative of Custodians of the Peace which represents some of those property owners, says she's never heard anyone make threats against the gas industry.

"We don't want to go that route," she said.

With files from The Canadian Press