The South African head of pressure group Greenpeace was arrested Friday after boarding an exploratory oil rig off western Greenland, dpa reported. "We have to draw a line somewhere and I say we draw that line here today," Kumi Naidoo, executive director of Greenpeace International, said in a statement issued just before he boarded the rig. Naidoo and another activist were arrested after scaling the Leiv Eiriksson rig from a speedboat launched from a Greenpeace vessel, avoiding a Danish navy vessel. Greenpeace has in recent weeks staged two similar protests against test drilling in environmentally sensitive Arctic waters. Naidoo repeated the group's demands that rig operator, Scotland-based Cairn Energy, present contingency plans in case of an oil spill, and had with him a list of 50,000 names calling for the company to cease drilling. Most of the 20 activists who were earlier arrested after scaling the rig in two earlier actions have since been deported from Greenland. Authorities in Greenland have previously criticized the Greenpeace action, saying Greenland, which in 2009 gained more autonomy from Denmark, had a right to exploit its natural resources for the benefit of its population.