ROCKVILLE, MD - MARCH 13: Contemplatively looks out the car window during a planning meeting with staff, Vice President Joe Biden is driven back to the White House after speaking to lawmakers, woman against violence advocates, and constituents concerning reducing domestic violence homicides in Rockville, Maryland, on Wednesday, March 13, 2013. (Photo by Melina Mara/The Washington Post) (Melina Mara/The Washington Post)

Environmentalists have seized on a comment Vice President Biden made while working a rope line in Columbia, S.C., on Friday, in which he told an activist he is "in the minority" within the administration when it comes to opposing the Keystone XL pipeline.

Elaine Cooper, who serves on the executive committee of the Sierra Club's South Caroline chapter, said in an interview Wednesday that Biden shared his thoughts with her during Rep. James Clyburn's (D-S.C.) annual fish fry.

Buzzfeed first reported the vice president's remarks late Tuesday, based on an e-mail a colleague of Cooper had sent to fellow environmentalists.

Cooper, who was wearing a black-and-white leather hat, said she attracted the vice president's attention and was able to ask him about the controversial proposal to ship heavy crude oil from Canada to U.S. refineries on the Gulf Coast.

" 'Sir, do you support rejecting the Keystone pipeline?' " Cooper recalled asking Biden. "And he responded, 'Yes, I do support rejecting the Keystone pipeline, but I'm in the minority.' And he smiled back at me."

An official in the vice president's office, who asked not to be identified, declined to discuss the details of the exchange between Biden and Cooper but wrote in an e-mail that the vice president was awaiting the results of the State Department's review of the project. The agency, which has jurisdiction over pipeline permits that cross international borders, is in the midst of finalizing an environmental review of the proposal and then must determine whether the project is in the national interest.

"The vice president has made his views known on this issue and his views haven’t changed. Any impression to the contrary would be mistaken," the official wrote. "For instance, he said of the project in an interview last year, 'It’s going to go through the process and the decision will be made on an environmentally sound basis.'”

Environmentalists are pressing the Obama administration, which must decide whether to grant TransCanada the right to build the pipeline, to reject it on the grounds that it will accelerate climate change and could lead to damaging spills affecting sensitive habitat. Backers say it will enhance America's energy supply and create short-term construction jobs.

Several environmental groups are trying to use Biden's comment to pressure other members of the Obama administration. The "All Risk No Reward" coalition has bought ads on Politico's homepage Thursday first showing images of the recent oil spill in Arkansas, and then Biden and Secretary of State John Kerry holding hands as they confer.

"Psst ... You should oppose Keystone XL too," the ad reads. "Tell President Obama and Secretary Kerry: Joe Biden is Right."

Sierra Club Executive Director Michael Brune praised Cooper for pressing Biden to state publicly where he stands on the project.

"Volunteers like Elaine Cooper are a testament to the strength of the Sierra Club and the movement against tar sands.  It's encouraging to hear about Vice President Biden's comment against the Keystone XL pipeline. In the meantime, stopping the Keystone XL pipeline remains a top priority for the Sierra Club, and we will continue to call on the president to reject dirty tar sands and go all in on clean energy."