Activists launched an online video game on Monday to attack leading politicians' support for development of Canada's oil sands, which greens portray as a crime against nature.

Tar Nation, which is set on the grounds of a dirty refinery, allows players to spray oil at Canadian Prime Minister Stephen Harper and opposition leader Michael Ignatieff to get them out of the tar sands.

Once the two men have been blasted with enough oil, the game ends and up pops an pre-written protest email addressed to the two leaders.

Harper and Ignatieff both back development of northern Alberta's vast oil sands, the world's second-largest proven reserves after Saudi Arabia, which require energy-intensive methods to extract and process crude. As a result, Canada's greenhouse gas emissions are soaring.

The game -- available at as well as Facebook and online gaming sites -- was dreamed up by the left-leaning Polaris Institute think tank.

The tar sands industry is Canada's fastest-growing carbon emitter -- our own built-in global warming machine, generating three times the greenhouse gas emissions as conventional oil production does, said the institute's Tony Clarke.

The tar sands machine perpetuates our dependence on dirty fossil fuels and prevents us from making the urgent and necessary transition to renewable energy sources and a clean energy economy, he told a news conference.

Harper, who says the oil sands mean Canada is a global energy superpower, has promised investment in technology that could cut emissions.

(Reporting by David Ljunggren; editing by Peter Galloway)