TORONTO - Canadian police broke up an occupation by environmental activists of an oil-sands processing facility under construction in Alberta, majority owned by Royal Dutch Shell Plc, arresting 16 activists over the weekend.

Environmental group Greenpeace and the company said on Sunday that the protest began on Saturday at an expansion of Shell's Scotford facility in Fort Saskatchewan, Alberta. It was the third such action in recent weeks to target facilities linked to oil sands production.

Greenpeace said 19 activists moved on to the site of an under-construction upgrader expansion to protest "the climate crimes of the tar sands." Upgraders are part of the process that converts tar-like bitumen mined from the oil sands into usable crude.

Shell had said that production at the rest of the plant was not affected.

A statement from the environmental group on Sunday said police had arrested the last nine activists and 16 in all were taken into custody. Greenpeace said charges may include breaking and entering, trespass and mischief.

Shell confirmed in a separate release on Sunday that Canadian police took activists into custody overnight, ending the protest. The company said it was concerned about the security breach and would tighten site access.

The energy giant had previously said that no construction was going on when the protesters entered the site. The upgrader is also owned by Marathon Oil Corp and Chevron Corp.

The protest comes after environmental activists last month canoed into Suncor Energy Inc's oil sands operation in northern Alberta, blocking equipment.

In another incident, protesters chained themselves to equipment at a Shell oil sands mine in northern Alberta to highlight what they view as excessive greenhouse gas emissions from the region's oil production operations.

Reporting by Jeffrey Hodgson; Editing by Cynthia Osterman