Two Greenpeace activists have been arrested by the Russian coastguard after their peaceful protest was met with violent opposition.
The pair had climbed onto a Russian arctic oil platform owned by state oil and gas company Gazprom to highlight the threat posed by drilling in the region.
Activists said that the coastguard tried to board Greenpeace ship the Arctic Sunrise but were refused permission by the captain.
The masked Russians fired 11 warning shots across the ship and threatened to fire at the icebreaker itself if it didn't leave, crew members reported.
Greenpeace Arctic oil campaign head Ben Ayliffe said: "Employing this level of force against a peaceful protest ship is completely disproportionate and should stop immediately."
Five inflatables set off from the Arctic Sunrise for the Prirazlomnaya platform early this morning but all climbers were removed by the afternoon.
Activists including Greenpeace executive director Kumi Naidoo occupied the same platform in August 2012.
The environmental organisation warns that drilling in the area - expected to start in 2014 - would put three nature reserves protected by Russian law at risk of oil spills.
Mr Ayliffe said: "It's clear that oil companies receive special protection from the Russian authorities, who seem more interested in silencing peaceful activists than protecting the Arctic from reckless companies like Gazprom.
"Let's be absolutely clear about this: the real threat to the Arctic comes not from Greenpeace International but from oil companies like Gazprom