The Harper government has approved construction of the proposed $7.9-billion Northern Gateway pipeline, setting up a fierce political battle over resource development in Canada that should persist into the 2015 election.

The federal approval Tuesday is a major step forward for the proponent, Calgary-based Enbridge, but clouds of uncertainty continue to hang over the controversial initiative. It would pipe Alberta oil sands through northern B.C. to the Pacific and then through coastal waters in supertankers.

Ottawa's decision puts B.C. Premier Christy Clark at the centre of a looming federal fight after Stephen Harper's chief political rivals in the NDP and Liberals each vowed to kill the controversial project should they win power next year, citing the danger of spills. Northern Gateway's construction is not expected to begin before the next federal ballot.

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NDP Leader Thomas Mulcair warned of civil unrest, suggesting Northern Gateway posed a "severe threat to social order, social peace," and Liberal Leader Justin Trudeau accused the Harper government of being a "cheerleader for this pipeline from the very beginning when Canadians needed a referee."

While the Conservatives had previously championed this project, the government failed to provide even one minister to explain or defend the decision Tuesday – an apparent effort to redirect attention to an arms-length regulatory panel that recommended approval last December.

First Nations leaders and environmentalists in British Columbia vowed to launch legal challenges, saying the review process was rigged from the start to obtain the result Mr. Harper wanted. They promised to keep up the political pressure, with direct action to block the project if necessary.

In a statement, federal Natural Resources Minister Greg Rickford said approval is subject to Enbridge satisfying 209 conditions – including further consultations with First Nations – laid down by the review panel. He noted the company must obtain construction permits from the B.C. government, which has laid out its own five conditions the company must meet.

"The proponent clearly has more work to do in order to fulfill the public commitment it has made to engage with aboriginal groups and local communities along the route," Mr. Rickford said.

Mr. Harper has long argued Canada must have access to West Coast ports for its booming oil sands industry, a conviction that hardened after the Obama administration delayed a decision on whether to approve the Keystone XL pipeline that would run from Alberta to the U.S. Gulf Coast. Before the Gateway decision's release Tuesday, Mr. Harper told the Commons his government would not approve a resource project "unless we can determine that it is safe for the environment and safe for Canadians."

B.C. Environment Minister Mary Polak said four of B.C.'s conditions still have not been met and Enbridge has much to do to satisfy those. She said her officials are still working with Ottawa around promised changes to marine oil cleanup and pipeline safety, and would not say when her government will say if those measures will be enough to meet B.C.'s demands for "world-leading" safety protocols.

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As for the B.C. government's demand for a "fair share" of the economic benefits of any pipeline, she said the province regards it primarily as a burden on industry, and she is "not aware of any live proposal" from Enbridge to satisfy B.C.

Alberta Premier Dave Hancock called Ottawa's green light for Northern Gateway a step forward for Canada, saying the project is critical to diversifying this country's economy and paying for goods and services, such as health care.

Northern Gateway would deliver 525,000 barrels per day of diluted bitumen to export terminals in Kitimat, B.C., where it would be loaded onto supertankers for export to Asia-Pacific markets. As part of the 209 conditions, Enbridge must sign up firm commitments from producers to ship on the pipeline – but the ongoing uncertainty over the project may undermine that effort.

Enbridge chief executive Al Monaco welcomed federal approval but acknowledged the company has much to do. Enbridge says it has agreements with 26 aboriginal communities along the pipeline route, but none has stepped forward to be identified.

First Nations on the coast remain adamantly opposed, fearing spills will wreak serious damage on their environment and livelihoods. "As far as we're concerned," said Art Sterritt, executive director of Coastal First Nations, an umbrella group representing nine communities, "Northern Gateway is a dead project and we will treat it as such and do whatever we can to make sure that it never moves forward."

With reports from Justine Hunter in Victoria and The Canadian Press