A proposed pipeline to bring oil from Canada's tar sands to the US Gulf Coast would have "no significant impact" on the environment, Washington has said, sparking disbelief from activists.
In a long-awaited environmental impact statement on the massive Keystone XL project, which has prompted repeated protests, the US State Department said the pipeline would be safer than most current oil transport systems.
"There would be no significant impact to most resources along the proposed pipeline corridor," Assistant Secretary of State Kerri-Ann Jones told reporters upon the release of the report.
Jones said the report, which is one step in the regulatory process, does not indicate approval or denial of the massive pipeline. US officials are due to make a final decision later this year after further review and hearings.
"This is not a lean in any way toward one particular decision or another," said Jones, the assistant secretary for Oceans and International Environmental and Scientific Affairs.
The report said that with extra precautions planned, the pipeline "would have a degree of safety greater than any typically constructed domestic oil pipeline system under current regulations."
It also said that scrapping the pipeline would have its own environmental costs, because refineries in the United States would then need to transport oil by other means such as trucks, railroads, barges and marine tankers.
The report did cite some potential problems in the event of a spill in "environmentally sensitive areas," including wetlands, rivers and other water resources, as well as areas with a high concentration of plants and wildlife.
As to a possible alternate route for the pipeline, the report said it "did not find any of the major alternatives to be preferable."
Canada has strongly backed the project and welcomed the report.
"Canada is the United States' largest and most reliable energy supplier," Natural Resources Minister Joe Oliver said in a statement.
"The Keystone XL pipeline will help to ensure that North America's future energy needs are met in a safe and environmentally responsible manner for decades to come."
Environmental groups have protested the pipeline because of its starting point in the oil sands of Alberta, Canada, where high-energy extraction produces a large volume of greenhouse gasses.
They have called on US President Barack Obama to deny a permit for the $7 billion project, due to stretch across 1,700 miles (2,700 kilometers), part of the broader $13 billion Keystone pipeline system.
Environmentalists were quick to denounce the report, issued after dozens of people were arrested in a protest outside the White House last weekend.
"It is utterly beyond me how the administration can claim the pipeline will have 'no significant impacts,'" Susan Casey-Lefkowitz of the Natural Resources Defense Council said.
Erich Pica, president of Friends of the Earth, said the pipeline decision poses a key test for Obama.
"If he sides with greedy oil companies instead of people and the climate, he will essentially be urging a huge part of his base to sit out the election," he said in a statement.
"With this supposedly final review of the pipeline's environmental impacts, the State Department has let him down by once again trying to sweep the serious dangers posed under the rug."
Pipeline operator TransCanada meanwhile said the report backs earlier studies and is part of an "exhaustive and detailed review" of the project.
The review "reaffirms the findings of the two previous environmental impact statements," said Russ Girling, TransCanada's president and chief executive officer.
"Today's final environmental impact statement continues to demonstrate the focus on safety and the environment that has gone into the development of this critical North American pipeline."
The company said Keystone XL would contribute more than $5 billion in property taxes to the communities it will pass through.
The building of the pipeline will also put 20,000 Americans to work, providing a $20 billion stimulus to the hard-hit US economy.