The New York-based watchdog Human Rights Watch (HRW) has urged the Russian authorities to immediately release 30 detained Greenpeace activists.
In a statement issued on October 1, HRW Russia researcher Tanya Cooper called a Russian threat to charge the activists with piracy "a grotesque distortion of the law."
Thirty members of the environmental group were detained last month when two members tried to scale a Russian offshore drilling platform in Arctic waters.
The next day, the Russian Coast Guard seized Greenpeace's ship, the "Arctic Sunrise," and towed it to Murmansk with the crew and activists aboard.
A court in Murmansk ordered the activists to be held in jail for two months as authorities investigate the case.
No charges have been brought against any of the activists.