DES MOINES, Iowa -- Hillary Rodham Clinton is breaking her longstanding silence over the construction of the Keystone XL pipeline, saying at a campaign stop in Iowa that she opposes the controversial project.

Clinton says the project has been a distraction and she doesn't believe it's in the best interest of "what we need to do to combat climate change."

The former secretary of state had previously said she shouldn't take a position on the issue, saying she didn't want to interfere with the Obama administration's deliberations.

But she has expressed her impatience in recent weeks over the pipeline issue. The pipeline is vigorously opposed by environmental activists.

Keystone XL would carry about one-quarter of the oil Canada exports to the U.S. each day, and ease potential bottlenecks on rail lines, but its U.S. opponents argue that it would help develop one of the world's dirtiest sources of oil.