President Barack Obama on Friday blocked the construction of a controversial Keystone XL oil pipeline between Canada and the United States, ending years of bitter and politically charged debate.
Obama said the plan "would not serve the national interests of the United States," doing nothing to build "meaningful, long-term" economic growth, lower gas prices or help the environment.
Opponents have argued that bringing tar sands crude 1,179 miles from Alberta to the Gulf of Mexico would do little for U.S. jobs and would hurt the environment.
TransCanada first applied for permission to build the pipeline years ago.
But until now, Obama's White House has refused to take a public stance, ignoring a clamor of demands from environmentalists, the oil lobby and opposition Republicans who favor the plan.
In recent weeks Democratic presidential candidate Hillary Clinton - who once led the review as secretary of state - said it should not be approved.
Clinton had used her former position as a rationale for not weighing in, saying she wanted Obama's administration to finalize its assessment on the project.
But during a campaign event in Iowa in September, she described Keystone as "a distraction from the important work we have to do to combat climate change, and, unfortunately from my perspective, one that interferes with our ability to move forward and deal with other issues."
Obama's announcement comes just days after the swearing-in of new center-left Canadian Prime Minister Justin Trudeau - and after TransCanada tried to halt the review process.
That move was rejected by U.S. government lawyers, and now appears to have been an attempt to avert outright rejection.
TransCanada shares fell around 5 percent on the news.
The announcement also comes weeks before Obama is expected to travel to Paris to help ink a global climate accord aimed at limiting carbon emissions worldwide.