Greenpeace
Greenpeace activists being shadowed by Russian Coast Guard Greenpeace

Russian authorities on Thursday stormed a Greenpeace vessel, an icebreaker known as Arctic Sunrise that was circling an oil platform, a day after activists were arrested for scaling the platform, which is in the Barents Sea north of Russia, Greenpeace said on its website.

Greenpeace crew members said that Russian authorities rappelled onto the ship from a helicopter with guns drawn. Crew members locked themselves in the communications room, where they had been tweeting up until the ship lost contact with Greenpeace.

They're almost in the room. This could be our last tweet for awhile. Thanks for all your support, don't stop now! #Savetharctic

On Wednesday, activists from the Arctic Sunrise, Greenpeace's icebreaker, sent five vessels to the Prirazlomnaya platform, which is operated by Kremlin-controlled OAO Gazprom (MCX:GAZP), triggering gunfire -- at least 11 shots were fired -- from the Coast Guard at the Arctic Sunrise, it was reported.

"Due to the refusal of the Arctic Sunrise captain to halt the unlawful activity, the administration took a decision to stop the ship. The Coast Guard was forced to fire warning shots four times from an artillery cannon onboard a vessel," the Russian Federal Security Service said.

The Russian Coast Guard is holding the Greenpeace activists in the mess hall of the Arctic Sunrise, Greenpeace said on Twitter.

The Arctic Sunrise has repeatedly traversed the Arctic by working on various issues that deal with climate change and protection of the environment from potential oil spills.