A federal appeals court panel has affirmed a lower court decision that ordered environmental activists to stay away from Shell drilling ships.

U.S. District Judge Sharon Gleason has ordered Greenpeace USA to stay a kilometer away from Shell drill ships destined for the Alaska Arctic through October 2012.

Shell sought the injunction after Greenpeace New Zealand activists boarded the drill ship Noble Discoverer before it left for the U.S. West Coast.

A divided three-judge panel of the 9th U.S. Circuit Court of Appeals found "ample support" that Greenpeace USA had undertaken or supported tactics including "forcible boarding" of vessels or use of human beings to impede drilling.

Judge Milan Smith Jr., dissented in part, saying he couldn't support sanctions on Greenpeace USA based largely on the conduct of sister groups.