DULUTH -- Enbridge Energy Corp. received a permit Thursday to build its Alberta Clipper oil pipeline from Canadian oil fields to Superior, Wis., and company officials said they could start construction as early as today.

The permit, signed by U.S. Secretary of State Hillary Clinton, was the last major hurdle the company needed to clear to build the pipeline that will carry tar-sands oil from Alberta, across northern Minnesota to Superior and beyond.

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Another pipeline would carry refined products back to Canada for use in diluting the thick tar-sands oil.

The massive pipeline project already has been approved by the Minnesota Public Utilities Commission and appears ready for construction to begin.

The pipeline would carry about 450,000 barrels of oil, or 19 million gallons, a day. That would be in addition to the 1.6 million barrels a day that the company already moves through an existing pipeline along the same route.

The $1.2 billion U.S. segment of the pipeline is part of an $8 billion expansion. From Superior, the oil could either be refined at the Murphy Oil facility or piped 450 more miles to Illinois.

The project will create more than 1,200 jobs for the stretch of pipeline from Clearbrook through Bemidji to Deer River, with Bemidji as a staging area.

A federal Environmental Impact Statement on the project became final July 6, ending a lengthy public comment period. The State Department was the lead agency because the pipeline crosses an international border.

A spokeswoman for Houston-based Enbridge said construction could start as early as today.

The project is opposed by Minnesota and national environmental groups and by some members of the Leech Lake and Fond du Lac reservations, although elected officials of those bands have approved the project crossing their reservations.

Opponents of the pipeline say that the oil is among the dirtiest in the world and that mining it from tar sands is damaging the environment for native tribes in Canada. It's blamed for leaving scarred landscapes and polluted waters in northern Alberta. Tar sand oil also is high in carbon dioxide, a greenhouse gas, and requires more energy to process, opponents say. They also claim the pipeline will harm wetlands in Minnesota and Wisconsin.

Earlier this year the Minnesota Center for Environmental Advocacy filed multiple lawsuits against the pipeline for many of the same reasons. Those suits still have not been decided, but no court order is in place at this time that would prevent construction from starting.

"The National Interest Determination took many factors into account, including greenhouse gas emissions," according to a statement from the State Department issued Thursday. "The administration believes the reduction of greenhouse gas emissions are best addressed through each country's robust domestic policies and a strong international agreement.

"The United States is taking unprecedented steps at home to transform how we produce and consume energy. The president is committed to reducing overall emissions and leading the global transition to a low-carbon economy," the statement said.

Along with calling Canada "a stable and reliable ally" and that the agreement will "augment the security of this energy supply," the State Department noted that "approval of the permit sends a positive economic signal, in a difficult economic period, about the future reliability and availability of a portion of United States' energy imports, and in the immediate term, this shovel-ready project will provide construction jobs for workers in the United States."

"The State Department has rubber-stamped a project that will mean more air, water and global-warming pollution, particularly in the communities near refineries that will process this dirty oil," said Earthjustice attorney Sarah Burt. "The project's environmental review fails to show how construction of the Alberta Clipper is in the national interest. We will go to court to make sure that all the impacts of this pipeline are considered."

Construction work will be done by Global Pipeline Partners, a partnership of Michels Corp. of Brownsville, Wis., Precision Pipeline of Eau Claire, Wis., and U.S. Pipeline of Houston. Enbridge has estimated that as many as 3,000 workers may be on the job during peak construction.

Bemidji Pioneer Political Editor Brad Swenson contributed to this report. John Myers is a staff writer for the Duluth News Tribune, a Forum Communications Co. newspaper, which also owns the Bemidji Pioneer.