An unidentified protester holds a banner during Greenpeace's occupation of Shell's operation in Fort Saskatchewan, Alta., on Saturday. (Greenpeace)

About 20 Greenpeace activists stormed a Shell Canada upgrader expansion site northeast of Edmonton on Saturday.

The protest in Fort Saskatchewan is the latest attempt by Greenpeace to shed light on what it calls the "climate crimes of the tarsands."

The group says activists from Canada, France, Brazil and Australia have scaled an under-construction upgrader, which upgrades heavy oil into a lighter synthetic oil that can be refined into gasoline and other products.

Three Greenpeace activists have been arrested. More than a dozen are occupying three smokestacks under construction and a crane, the group said.

Melina Laboucan-Massimo, a Greenpeace activist who was outside the Scotford upgrader expansion site, said protesters have climbed the stacks and crane to unfurl banners that say "Climate SOS."

She said the protesters are willing to stay as long as it takes to get their message out.

"There's no way to process … oil in a clean way," Laboucan-Massimo said. "It's dirty, dirty oil. It's the bottom of the barrel that we are dealing with here.

"We definitely need to turn away from tarsands expansion and turn towards investment in clean, renewable energy. These solutions are available to us now. It's just a lack of political will that's not being there to create a green, just world that we really need for our future generations."

Greenpeace's 3rd recent Alberta protest

Shell said in a statement that it wished Greenpeace "and all others who have concerns with our activities would talk to us face to face instead of using confrontation and unsafe tactics."

The company said it was "developing an important resource that society needs, and doing it safely, responsibly and in compliance with all laws and regulations."

This is the third action Greenpeace has undertaken in Alberta in recent weeks.

On Sept. 16, Greenpeace activists chained themselves to two massive oilsands trucks in Shell's Albian Sands mine, north of Fort McMurray.

On Sept. 30, about 20 protesters were arrested after blocking work at Suncor Energy's open-pit mine in northern Alberta.

With files from The Canadian Press