Police arrested nearly 400 student-led demonstrators who marched to the White House on Sunday to protest against the Keystone XL pipeline.
Marching under the name XL Dissent, at least 500 students from across the United States demonstrated and engaged in acts of civil disobedience outside the White House.
After repeated warnings, police arrested demonstrators for "blocking passage" of sidewalks, Sgt. Lelani Woods of the U.S. Park Police told Al Jazeera. "We advised protesters of the outcome of the warnings, which would be an arrest. They decided to remain on the sidewalk, so the arrest process began," she said.
Some protesters fastened themselves to the White House fence with plastic zip ties, and others staged a sit-in and mock oil spill on the sidewalk outside the White House, said Keith Wrightson, who was at the scene.
About 200 more protesters stood across the street holding signs, Wrightson told Al Jazeera by phone. "Individuals were arrested in groups of five roughly every 10 minutes," he said.
The controversial Keystone XL pipeline, which must be approved by President Barack Obama before completion, is viewed by many environmentalists as a litmus test of Obama's commitment to green issues and, indirectly, to fighting climate change.
The 1,179-mile pipeline would carry a type of thick crude oil from Canada's tar sands, in the province of Alberta, across parts of eight states and over the vast Ogallala Aquifer, to U.S. refineries in Nebraska, Illinois and the Gulf Coast of Texas.
Opponents say the pipeline project would harm the environment and could threaten the health of communities living near the pipeline as well as those dependent on the aquifer because of the possibility of leaks and ruptures, leading to hard-to-clean and potentially hazardous oil spills.
The website for Sunday's demonstration warned of the danger of "environmental devastation" and said the pipeline "would carry over 800,000 barrels of tar sands oil, best described as a semi-viscous, carbon intensive, toxic injustice."
Proponents say the project would promote energy independence and create jobs.
While the southern leg of the Keystone XL pipeline has already begun operations, plans for the northern section are on hold, pending a presidential permit.
A recent study published by the Center for Biological Diversity found that the pipeline would cause damage to wildlife habitats it crosses. The organization criticized the U.S. State Department for not considering the impact on endangered species.
Those concerned by a warming climate cite the dangers of tar sand oil's higher greenhouse gas emissions compared with conventional crude's.