Armed Russian officials have boarded a ship and arrested activists, including six Britons, protesting against oil drilling in the Arctic, Greenpeace said.
The environmental group's vessel Arctic Sunrise is in the remote Pechora Sea in the Russian Arctic, near to Russian oil company Gazprom's Prirazlomnaya oil platform to protest against its attempts to drill for oil in the region.
Greenpeace said the Russian coast guard abseiled onto the Arctic Sunrise from helicopters and arrested 25 protesters on-board, including six UK nationals.
In a tweet from the icebreaker, activists said armed guards were attempting to kick down the door of the communications room. They also tweeted: "Latest from the deck: Crew are sitting on their knees on the helipad with guns pointed at them."
A short time later, contact with the ship was lost, Greenpeace said. It claims the Arctic Sunrise was boarded illegally, as the ship was inside Russia's exclusive economic zone (EEZ) in which foreign vessels should be free to navigate.
Two activists had already been arrested by the coastguard for a protest in which they scaled the Gazprom oil rig.
Greenpeace is campaigning against attempts by oil companies to extract oil from the waters of the Arctic, warning a spill would be highly environmentally damaging and that extraction of more fossil fuels will add to climate change.
The environmental group said Gazprom's plans to start drilling from the Prirazlomnaya platform in the first quarter of 2014 raised the risk of an oil spill in an area that contains three nature reserves protected by Russian law. Activists including the organisation's executive director, Kumi Naidoo, occupied the same platform in August 2012.
Mr Naidoo said: "This illegal boarding of a peaceful protest ship highlights the extreme lengths that the Russian government will go to to keep Gazprom's dangerous Arctic drilling away from public scrutiny.
"We ask President (Vladimir) Putin to restrain the coast guard and order them to holster their guns and withdraw. We are a peaceful organisation and our protest has done nothing to warrant this level of aggression."