CALGARY, Alberta, July 24 (Reuters) - Protesters blocked a pipe to a waste-water pond at an Alberta oil-sands mine operated by Syncrude Canada Ltd on Thursday and demanded a halt to rising production that critics say is devastating the region's environment, Greenpeace said on Thursday.

Greenpeace said in a release that 10 activists put a cap on the pipe at the Aurora North mine at Syncrude's project site near Fort McMurray in northern Alberta.

Protesters also raised a banner that read "World's Dirtiest Oil: Stop the Tar Sands," and put a skull-and-crossbones flag atop yet another pipe into the tailings pond.

The environmental group is calling for the Alberta government to stop approving new projects to exploit the region's oil sands, which hold the biggest petroleum reserves outside the Middle East.

Oil companies are expected to spend more than C$100 billion to nearly triple production from the region -- to more than 3 million barrels day -- by 2015.

"It's time for the government to step in and start saying no to these companies and to put the brakes on development," said Mike Hudema, a tar sands campaigner at Greenpeace.

The tailings pond at the mine owned by Syncrude, the biggest oil sands producer, focused global attention on the environmental costs of producing the region's tarry bitumen deposits when 500 ducks died after landing on the pond earlier this year.

Heavy metals and other toxins are a byproduct when the tarry bitumen is separated out from oil sands using water, which is sent to settle in waste-water, or tailing, ponds.

Alberta regulators plan to tighten rules for the toxic ponds, requiring developers of oil-sands projects to prepare operations and abandonment plans for the ponds and submit them for the regulator will review.

It would also force companies to file schedules for pond construction, use, closure and other milestones with regulators, or face penalties if the rules are broken.

However Greenpeace is also calling rules requiring the clean up of existing tailings ponds and stiffer penalties for environmental infractions.

Syncrude could not immediately reached for comment.

Syncrude is a joint venture owned by Canadian Oil Sands Trust <COS_u.TO>, Imperial Oil Ltd <IMO.TO>, Petro-Canada <PCA.TO>, ConocoPhillips <COP.N>, Nexen Inc <NXY.TO>, Nippon Oil Corp <5001.T> unit Mocal Energy Ltd. and Murphy Oil Corp <MUR.N>. (Reporting by Scott Haggett; Editing by Frank McGurty)

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