NEW YORK • Ending years of declining to take a side on the issue because of her role in the Obama administration, Mrs Hillary Clinton on Tuesday announced her opposition to the construction of the Keystone XL oil pipeline.

"I don't think we need to have a pipeline bringing very dirty oil, exploiting the tar sands in western Canada, across our border," she told the Des Moines Register's editorial board.

At a town hall in Des Moines beforehand, she expressed an eagerness to end the seven-year debate over Keystone, which had become a "distraction" from the broader fight against climate change.

"I don't think it's in the best interest of what we need to do to combat climate change," she said in response to a question from a Drake University student.

Since leaving the State Department in early 2013, Mrs Clinton had insisted that she would not take a position on the pipeline permitting process, as it began while she led the agency.

But with the administration's process dragging on, and facing constant questions about the issue on the campaign trail as well as pressure from her Democratic rivals, Mrs Clinton decided that she needed to speak out. "I thought this would be decided by now, and therefore I could tell you whether I agree or disagree," she said. "But it hasn't been decided and I feel now I've got a responsibility to you and to voters who ask me about this."

During the town hall, Mrs Clinton said that she will unveil proposals for "a North American approach to fighting climate change and clean energy" in the coming days.

Environmental advocates characterised Mrs Clinton's stance as a policy evolution. On the other side of the aisle, the American Petroleum Institute characterised Mrs Clinton's position as running against the grain of public opinion.

BLOOMBERG