More than 100 demonstrators were arrested Monday for storming the Canadian parliament to protest Ottawa's support for a proposed pipeline to bring oil from Canada's tar sands to the US Gulf Coast.

Waves of environmentalists and aboriginals breached a police barricade around the neo-Gothic building to try to hold a sit-in inside as a crowd of 400 chanted "Let them pass!"

But they were quickly handcuffed and whisked away to a waiting police bus, and charged with trespassing before being released, Royal Canadian Mounted Police spokesman Sergeant Marc Menard told AFP.

The indictment carries a fine of $65 "and the demonstrators agreed to stay away from the parliament building for one year," he said. The first 17 to be arrested faced obstruction charges, which carries a maximum penalty of up to two years in prison, but the citations were later downgraded.

"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 protestor Clayton Thomas-Muller of the Indigenous Environmental Network.

"Our communities should not be sacrificed on the altar of the US's addiction to dirty fossil fuel."

The rally against the Keystone XL pipeline follows a similar protest in Washington in August.

Canada strongly backs 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), and 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.

Federal police said the Ottawa event was "orderly and peaceful" as protestors formed neat lines to climb over the police fence using stepladders on either side provided by authorities so nobody would injure themselves.

The mass civil disobedience was organized by Greenpeace and won the support of 25 other environmental groups and aboriginal tribes, as well as 34 celebrities such as actors Tantoo Cardinal ("Dances with Wolves") and Kate Vernon ("Battlestar Galactica").

Natural Resources Minister Joe Oliver rejected their criticisms, saying the Canadian government "firmly believes that it is in our collective national interest for the pipeline to proceed."

If the Keystone XL pipeline is approved, he said, it will generate over 140,000 Canadian jobs and $600 billion in economic activity over the ensuing 25 years.

"Our government will continue to promote Canada, and the oil sands, as a stable and secure source of energy to the world, and will defend Canadian jobs and interests," Oliver said.