At least 65 protesters were arrested Saturday outside the White House during a sit-in demonstration denouncing a proposed pipeline that would transport crude oil from the Alberta oilsands to a refinery in Texas.

As the protesters shouted "hey-ho, Keystone XL has got to go," U.S. Park Police and SWAT team officers handcuffed protesters and removed them from the area.

Bill McKibben, a leading American environmentalist and one of the organizers of the two-week protest, was among those arrested.

U.S. President Barack Obama wasn't around to see Saturday's protest. He was vacationing with his family in Martha's Vineyard.

Organizers said at least 1,500 people have signed up to participate in a series of sit-ins, which are to continue until Sept. 3.

Calgary-based TransCanada's Keystone Pipeline is a 3,460-kilometre pipeline that transports crude oil from Hardisty, Alberta to U.S. markets centered around Illinois and Oklahoma. The Keystone XL would be an extension of the existing line to Houston, TX.

The protesters argue the oil is dirty and allege the site of the oilsands is the world's biggest emitter of carbon. They also fear that a leak in the Keystone XL pipeline could cause an environmental disaster.

A U.S. Park Police officer arrests a protester on Saturday. Manuel Balce Ceneta/Associated Press

In a YouTube video, Hollywood actor Mark Ruffalo urged opponents to "put your principles into action" and join the protests.

"This pipeline will travel over some of the richest farmland and most beautiful pristine wilderness on the continent and spills are inevitable," he says in the clip.

Organizers said Ruffalo wasn't at Saturday's protest, but plans to take part sometime in the next two weeks.

They said Canadian-born actress Margot Kidder plans to join the protest early in the week, along with her friend, Tantoo Cardinal, an aboriginal actress from northern Alberta.

Kidder, best known as the Lois Lane character from the 1980s Superman movies, is now an American citizen living in Montana.

The U.S. State Department is expected to release its final environmental analysis of the pipeline by the end of the month. President Barack Obama will then have 90 days to decide whether going ahead with the project would be in the national interest. The president is currently on holiday in the Massachusetts resort town of Martha's Vineyard.

Proponents say the pipeline plan will give the United States a reliable supply of oil at a time when imports from countries such as Mexico and Venezuela are declining.

Cindy Schild, the refining issues manager at the American Petroleum Institute, said in a recent review on the project that a U.S. government environmental assessment "has indicated this pipeline will exceed all other [safety] standards."

"The State Department has stated that it will be state-of-the-art," she told the U.S. television news program Democracy Now.