The activists are on a Greenpeace ship, the Arctic Sunrise, which was seized last week by the Russian Coast Guard and towed today into a port near Murmansk.
It was unclear how many of the 30 activists on board face piracy charges, which carry a potential prison sentence of up to 15 years and a fine of USD 15,500. The Investigative Committee, Russia's federal investigative agency, said it would question all those who participated in the protest and detain the "more active" among them.
"When a foreign vessel full of electronic technical equipment of unknown purpose and a group of people calling themselves members of an environmental rights organization try nothing less than to take a drilling platform by storm, logical doubts arise about their intentions," Investigative Committee spokesman Vladimir Markin said in a statement.
He said the activists posed a danger to the work of the oil platform. "Such activities not only infringe on the sovereignty of a state, but might pose a threat to the environmental security of the whole region," Markin said.
The Arctic Sunrise was anchored today in a small bay near Severomorsk, the home port of Russia's Northern Fleet, 25 kilometres north of Murmansk.
Greenpeace said the 30 activists were from 18 countries.