Russia on Thursday charged seven more Greenpeace activists and a Russian photographer with piracy over a protest in the Arctic, an offence that can carry lengthy prison terms, the group said.
Thirty mostly foreign crew members from Greenpeace's Arctic Sunrise ship have been held in custody for the past two months and on Wednesday 14 were charged with piracy.
Piracy by an organised group carries a sentence of between 10 and 15 years in Russia. Investigators have accused them of trying to seize property by force.
The Sept. 18 protest saw several activists scale Gazprom's Prirazlomnaya oil platform in the Barents Sea to denounce plans for drilling in the pristine Arctic.
Russian border guards then lowered themselves onto the Dutch-flagged Arctic Sunrise from a helicopter, locked up the crew and towed the icebreaker to Murmansk located nearly 2,000 kilometres north of Moscow.
On Thursday, investigators charged seven more activists and Russian freelance photojournalist Denis Sinyakov, who was working for Greenpeace on a freelance basis, Greenpeace said.
The detention of Sinyakov, a former AFP and Reuters staff photographer, last week prompted leading Russian media to show solidarity by blacking out photographs on their websites.
Investigators on Wednesday had already charged a British freelance videographer, Kieron Bryan.
It appeared likely that all 30 activists -- 26 of them foreigners -- would be handed the same charge, even though the detainees included the ship's support staff.
Greenpeace has called the charges an "outrage."
The group said Thursday that all the remaining activists had been brought in police vans to the investigators' office in the northern city of Murmansk above the Arctic Circle, meaning that they could all be indicted that day.
The lawyers of all 30 activists have filed appeals against the court decisions to hold them in detention, a spokeswoman for Murmansk's Lenin district court told the RAPSI legal news agency.
The chairman of the presidential council on human rights, an advisory body, Mikhail Fedotov, told the Interfax news agency on Thursday that there was "not the slightest basis" for the piracy charge.
President Vladimir Putin has said that in his opinion, the activists were not pirates but had breached international law.
Campaign groups including Human Rights Watch have called for their release.
The unusually tough charges for a protest sparked comparisons with the case of Pussy Riot punks who were last year sentenced to two years in a penal colony for a protest against Putin in a Moscow church.
"This all reminds me very much of the case of Pussy Riot," journalist Anton Orekh wrote on the website of popular radio station Moscow Echo.
"The whole world will rise up to defend them. And rightly so, because that's not justice but a reprisal."
Yet a poll carried out by state agency VTsIOM at the end of last month found that 60 percent of respondents thought Russia's actions were appropriate.
The activists are being held in pre-trial detention centres in Murmansk and the nearby town of Apatity.
A regional prisoners' rights activist told AFP this week the detainees were complaining of their holding conditions, including cold cells, chain-smoking fellow prisoners and difficulties communicating with guards, hardly any of whom speak English.
Greenpeace held a similar protest at the same oil platform last year without incurring any punishment.