Electric cars, often touted as "green" vehicles, might cause as much or more pollution than gasoline- or diesel-powered cars, European researchers say.

Greenhouse gas emissions can rise dramatically if coal is used to produce the electricity to charge cars, and electric car factories can emit more toxic waste than conventional car factories, researchers at the Norwegian University of Science and Technology said.

Writing in the Journal of Industrial Ecology, the researchers analyzed the life-cycle impact of conventional and electric vehicles, examining how the production, use and end-of-life dismantling of a car affect the environment.

"The production phase of electric vehicles proved substantially more environmentally intensive," than how gasoline and diesel cars are made, their report said.

"The global warming potential from electric vehicle production is about twice that of conventional vehicles."

Also, a lot of toxic minerals such as nickel, copper and aluminum are required in the manufacture of batteries and electric motors, the researchers said.