In a counter to Hillary Clinton, Keystone XL planner TransCanada said pipelines are the safest and least carbon-intensive ways to transport crude oil.

Democratic presidential candidate and former Secretary of State Clinton said from the campaign trail in Iowa the planned Keystone XL pipeline from Canada would be a "distraction" to the evolving fight against climate change.

"I do not think it is in the best interest of what we need to do to combat climate change," she said.

The Republican-led Congress that took its seat in January said passing legislation to approve construction of Keystone XL, offered for U.S. consideration more than six years ago, was job No. 1. The pipeline has become a scapegoat for U.S. energy policies, with backers touting its energy and economic benefits, while detractors say it's too environmentally risky to support.

Davis Sheremata, a spokesman for TransCanada, said there were tens of thousands of pages of studies showing the pipeline would have a minimal impact on the environment.

"Pipelines are the safest and least greenhouse gas-intensive way to transport needed Canadian and American crude oil to Americans," he said in an emailed statement.

A U.S. State Department review of the pipeline found some of the environmental issues would be prevalent with or without Keystone XL.

As Secretary of State, Clinton sparked controversy in 2010 when she said the United States was either going to get "dirty oil" from the Middle East or "dirty oil" from Canada.

The following year, Friends of Earth, the Center for International Environmental Law and Corporate Ethics International filed suit in a San Francisco court seeking documents related to Clinton's communications with Paul Elliott, a former manager for her 2008 presidential campaign who went on to serve as a lobbyist for TransCanada.

The environmental groups said Elliot had a "cozy relationship" with the State Department. An executive order gives the U.S. State Department vetting power over the pipeline and the Environmental Protection Agency said recently further considerations should be given because previous studies on the pipeline were conducted in a different economic climate.