Greenpeace has called on Russia to release a ship seized in the Arctic with 30 activists on board.
The Russian coastguard is towing the ship towards the city of Murmansk, a journey expected to take several days.
Four of the Greenpeace activists had tried to board a Gazprom oil rig on Wednesday, to protest against drilling.
Russia accused Greenpeace of violating an exclusion zone around the rig, but the group said its ship was in international waters.
Greenpeace published photos that it said showed Russian security personnel in balaclavas confronting the activists with guns and knives after abseiling from helicopters onto the Dutch-flagged Arctic Sunrise.
Greenpeace says planned drilling at Gazprom's Prirazlomnaya rig in the Barents Sea threatens a unique and fragile environment - a claim denied by Moscow.
"The safety of our activists remains our top priority and we are working hard to establish what is facing them," said Ben Ayliffe, head of Greenpeace International's Arctic oil campaign.
"They have done nothing to warrant this level of aggression and have been entirely peaceful throughout," he said.
Greenpeace dismissed claims that a safety pod on the ship in any way resembled a bomb.
The group of activists being held includes six Britons.
A spokeswoman for the Murmansk region's border guards told local media that the Arctic Sunrise's captain had already been questioned, and the activists were being taken to court for "further legal procedures".
The Russian foreign ministry earlier accused the group of "aggressive and provocative" behaviour.
Moscow also said that its coastguard vessel had to fire warning shots across Arctic Sunrise.
The Gazprom project is Russia's first effort to extract oil from the Barents Sea.
Prirazlomnaya is scheduled to begin production by the end of the year. Russia's economy and its recent growth depend to a large extent on income from its huge oil and gas deposits.