Hillary Clinton said Tuesday that she opposes the construction of the Keystone XL pipeline, calling it "a distraction" that "interferes" with other climate efforts.

"I think it is imperative that we look at the Keystone XL pipeline as what I believe it is -- 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," Clinton said in response to a question at a Des Moines, Iowa forum on Tuesday.

"Therefore, I oppose it. I oppose it because I don't think it's in the best interest of what we need to do to combat climate change."

The White House was briefed on Clinton's opposition to the pipeline before she made the comments today, according to a Clinton aide.

Last week, Clinton put the White House "on notice," expressing concern that the process had taken this long. She noted she could not "wait too much longer" to take a stance on the issue.

The former secretary of state has been evasive all year, even as a candidate, on the issue that has now animated environmentalists — both grassroots activists and influential donors — within the Democratic Party for years.

She has cited her previous role in the administration as a reason for her refusal to take a position previously, and, in July, said she didn't want to "second guess" President Obama.

"If it is undecided when I become president, I will answer your question," she said in July, when asked whether she would take a yes or no position on the pipeline.

As secretary of state in 2010, Clinton said the State Department was "inclined" to sign off on the pipeline, saying the only choices the U.S. had at the time were to get "dirty oil from the Gulf or dirty oil from Canada."

Opposition to the pipeline, which would originate in Canada, also includes many in the labor movement. Clinton, according to an aide, privately let labor officials know in recent weeks of her position.