© Agence France-Presse/Michel ComtePolice move in to arrest demonstrators who breeched a barricade during a protest in front of Canadian Parliament
And up to 200 more arrests were expected as scores of environmentalists and aboriginals lined up to breach a police barricade around the neo-Gothic building and hold a sit-in inside.
"The tar sands represent a path of broken treaties, eroded human rights, catastrophic climate change, poisoned air and water and the complete stripping of Canada's morality in the international community," said Clayton Thomas-Muller of the Indigenous Environmental Network.
"Our communities should not be sacrificed on the alter of the US's addiction to dirty fossil fuel."
The rally against the Keystone XL pipeline follows a similar protest in Washington in August, and was endorsed by 26 environmental groups and aboriginal tribes, as well as 34 celebrities including actors Tantoo Cardinal (Dances with Wolves) and Kate Vernon (Battlestar Galactica).
Canada has strongly backed the project and last month welcomed a US State Department report that said the pipeline would be safer than most current oil transport systems and would have "no significant impact" on the environment.
Environmental groups have protested the pipeline because of its starting point in the oil sands of Alberta, Canada, where high-energy extraction produces a large volume of greenhouse gasses.
They have called on US President Barack Obama to deny a permit for the seven billion dollar project, due to stretch across 1,700 miles (2,700 kilometers), which is part of a broader $13 billion TransCanada pipeline system.
US officials are due to make a final decision later this year after further review and hearings.
This is not what we in the US want and our main concern is the possible impact on the environment.