Greenpeace says armed Russian coast-guard officers have boarded its ship protesting oil exploration in the Arctic and arrested the crew, some 25 people according to outside reports.
The environmental group says the coastguard officers descended on to the Dutch-registered ship "Arctic Sunrise" on September 19 from a helicopter via ropes.
The ship's crew reported that the Russians were "breaking into the comms room now. Ship Twitter account may be silenced."
The group has reportedly since lost contact with the ship.
The "Arctic Sunrise" was said to be circling a Gazprom-owned platform in the Barents Sea, and according to activists it was within a "exclusive economic zone" where foreign vessels are allowed to sail.
One day earlier, the Russian coast guard arrested two Greenpeace activists when they tried to scale the the "Prirazlomnaya" oil platform.
Russia said earlier on September 19 that it had protested to the Dutch ambassador in Moscow over what it called the "aggressive and provocative" actions of the activists.
Last week, Greenpeace shared video of Russian authorities boarding the "Arctic Sunrise," an icebreaker, and ordering the crew to cease its activities.
Greenpeace says Gazprom intends to start production from the "Prirazlomnaya" platform in 2014, raising the risk of an oil spill.
"Prirazlomnaya" is Russia's first Arctic offshore rig.
Based on reporting by Reuters, EcoWatch, and AFP