Russia has charged Greenpeace activists who tried to board a state-owned offshore drilling platform in the Arctic with piracy.
It was unclear how many of the activists face piracy charges, which carry a potential prison sentence of up to 15 years and a fine of 500,000 roubles (about £9,500). 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.
Two activists tried to climb onto the Prirazlomnaya platform on Thursday and others assisted from small inflatable boats. The Greenpeace protest was aimed at calling attention to the environmental risks of drilling for oil in Arctic waters.
"When a foreign vessel full of electronic technical equipment of unknown purpose and a group of people calling themselves members of an environmental rights organisation try nothing less than to take a drilling platform by storm, logical doubts arise about their intentions," an Investigative Committee spokesman 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," he said.
Greenpeace insists Russia had no right under international law to board its ship. One activist said coast guard officers hit and kicked some crew when they stormed the vessel.
A Greenpeace spokesman said: "Peaceful activism is crucial when governments around the world have failed to respond to dire scientific warnings about the consequences of climate change in the Arctic and elsewhere.
"We will not be intimidated or silenced by these absurd accusations and demand the immediate release of our activists."
Greenpeace said the activists were from Argentina, Australia, Brazil, Britain, Canada, Denmark, Finland, France, Italy, the Netherlands, New Zealand, Poland, Russia, Sweden, Switzerland, Turkey, Ukraine and the United States.