Fourteen Greenpeace activists have been charged with piracy by the Russian authorities.
They were among a 30-strong crew on a Greenpeace ship that was protesting against oil drilling in the Arctic.
The group was arrested last month after two of the protesters tried to board an oil platform owned by the Russian state-controlled firm Gazprom.
Greenpeace has called the charges “irrational, absurd and an outrage”.
The 14 activists were taken from jail to the Murmansk office of the Investigative Committee, the Russian equivalent of the FBI.
There they were formally charged with “piracy of an organized group”, an offence that carries a 15-year prison sentence.
Those charged include Kieron Bryan, a freelance video producer from London; Anthony Perrett from Newport in Wales; Alexandra Harris, originally from Devon, and Philip Ball from Chipping Norton.
Greenpeace said more activists are expected to be formally charged on Thursday.
The group’s international executive director, Kumi Naidoo, said the charges were “extreme and disproportionate”.
“A charge of piracy is being laid against men and women whose only crime is to be possessed of a conscience. This is an outrage and represents nothing less than an assault on the very principle of peaceful protest,” Reuters news agency quoted Kumi Naidoo as saying.
Kumi Naidoo said the way Russian officials had treated the protesters represented “the most serious threat to Greenpeace’s peaceful environmental activism” since the bombing of the Greenpeace ship Rainbow Warrior in New Zealand in 1985, when the group was campaigning against French nuclear testing in the Pacific.
Russian President Vladimir Putin had previously said the activists were “not pirates”, but may have broken international law.
The Investigative Committee said earlier this week that peaceful aims would not justify what it has described as an “attack” that posed a threat to the rig and its personnel.
Last month the Greenpeace ship approached the Prirazlomnaya platform, Russia’s first offshore oil rig which is scheduled to start operating by the end of the year.
Two activists tried to climb up onto the platform and tie themselves onto it, in an attempt to draw attention to the issue of the expansion of oil and gas exploration in the Arctic Ocean.
They were detained after a short skirmish in inflatable dinghies in which armed Russian FSB officers in balaclavas fired warning shots into the water.
Greenpeace has released cameraphone images it says show the moment Russian security forces boarded the Arctic Sunrise ship.
The Arctic Sunrise ship, with its crew comprising 18 nationalities, was then towed to Murmansk.