OTTAWA -- Canada's spy agency says many members of the environmental and Indigenous communities see the federal purchase of the Trans Mountain pipeline as a betrayal, and suggests that could intensify opposition to expanding the project.

A Canadian Security Intelligence Service assessment highlights a renewed sense of indignation among protesters and clearly indicates the spy service's ongoing interest in anti-petroleum activism.

The Canadian Press used the Access to Information Act to obtain a heavily censored copy of the June CSIS brief, originally classified top secret.

Civil liberties and environmental activists questioned the rationale for CSIS's interest, given that opposition to the pipeline project has been peaceful.

CSIS spokeswoman Tahera Mufti stressed the spy service is committed to following the governing legislation that forbids it to probe lawful protest and dissent.

"While we cannot publicly disclose our investigative interests, we can say that it is important for the service to pose important analytical questions on these types of issues, such as the question of whether developments such as the purchase of a pipeline could give rise to a national-security threat to Canada's critical infrastructure."

Earlier this year, Kinder Morgan dropped plans to twin an existing pipeline that carries about 300,000 barrels of bitumen daily from Alberta to British Columbia. The federal government announced in late May it would buy the pipeline and related components for $4.5 billion.

The government intends to finance and manage construction of the second pipeline -- which would increase the overall flow of bitumen to 890,000 barrels a day -- and ultimately try to find a buyer.

The CSIS brief characterizes resistance to the pipeline project as a "developing intelligence issue."

"Indigenous and non-Indigenous opponents of the project continue to highlight the increasing threats to the planet as a result of climate change and the incompatibility of new pipeline and oil sands projects with Canada's 2015 commitment under the Paris Climate Accord," the brief says. "At the same time, many within the broader Indigenous community view the federal government's purchase and possible financing, construction and operation of an expanded bitumen pipeline as wholly incompatible with its attempts at Crown-Indigenous reconciliation."

The pipeline acquisition and commitment to complete the project is therefore "viewed as a betrayal" by many within both the environmental and Indigenous communities, CSIS says.

"Indigenous opposition at the grassroots level remains strong. In response to the federal purchase, numerous Indigenous and environmental organizations have restated their commitment to prevent construction."

The brief singles out the Treaty Alliance Against Tar Sands Expansion, noting it has signatories from over 50 North American First Nations in its bid to halt the project. It also features a May quote from Canadian environmental organization Stand.earth that the decision "will haunt the Trudeau government."

The intelligence brief was completed a little more than two months before the Federal Court of Appeal quashed government approval of the pipeline project due to inadequate consultation with Indigenous groups and failure to properly assess the effect of increased tanker traffic in the waters off British Columbia.

In the wake of the court ruling, the federal government ordered the National Energy Board to reassess the tanker issue and asked a former Supreme Court justice to oversee fresh consultations with Indigenous communities.

The CSIS brief notes there had been "no acts of serious violence" stemming from peaceful demonstrations and blockades at Trans Mountain facilities in British Columbia that resulted in the arrest of more than 200 people, or at smaller protests across the country.

However, the document includes a section titled "Violent Confrontations and Resource Development" that mentions past conflicts over shale-gas development in New Brunswick and a high-profile pipeline in North Dakota.

It is unclear, because of the redactions to the document, exactly what CSIS was looking at, said Josh Paterson, executive director of the British Columbia Civil Liberties Association, which has expressed strong concern about the spy service's monitoring of activists.

In the information that has been released, there is no suggestion of a threat to national security or critical infrastructure, of clandestine activities or of violence in relation to the Trans Mountain project, Paterson said.

"While some opponents of the pipeline were arrested during protest for breaching a court order, that was a matter for police and the courts, and was done out in the open -- it should not be a matter for our spy agency."

Given past interest on the part of security and police officials, the CSIS brief is not surprising, said Tegan Hansen, a spokeswoman for Protect the Inlet, an Indigenous-led effort against the pipeline and tanker project.

But she is curious as to why the spy service document makes reference to sabotage and violent physical confrontations.

"I'm not sure why they're trying to draw that connection with violence," Hansen said. "I'd be interested to know. But it's certainly not our intention to ever pursue violence."