Activists are calling for the release of two Australians detained aboard a Greenpeace icebreaker after armed Russian officers stormed it using helicopters and ropes.
Greenpeace says the Arctic Sunrise had been sailing peacefully when security forces illegally boarded and arrested its crew at gunpoint early on Friday morning.
The Department of Foreign Affairs and Trade (DFAT) is seeking information from Moscow about the incident, which occurred while the vessel was protesting against oil exploration in the Arctic.
Russia has accused Greenpeace of “aggressive and provocative“ behaviour, saying activists had attempted to “infiltrate” the Prirazlomnaya oil platform owned by Russia’s Gazprom energy giant in the Barents sea.
Greenpeace acknowledged activists had tried to get aboard the rig but denies their behaviour was aggressive.
On Thursday, the coastguard arrested two Greenpeace activists - from Finland and Switzerland - who had tried to attach themselves to the platform, and was still holding them on Friday.
Greenpeace Australia chief executive David Ritter said Australian Colin Russell and Alex Harris, a permanent Australian resident, are among the 28 activists detained on the Arctic Sunrise.
Ms Harris had managed to radio back an SOS just after the boat was stormed, Greenpeace says.
Activists said on the Twitter page of the Dutch-flagged boat described how men were “on board with guns”.
The Arctic Sunrise was three nautical miles inside international waters about 10-12 hours from the port of Murmansk in Russia’s northwest when it was boarded, Mr Ritter said.
A Greenpeace spokeswoman told AAP they had not had any contact with the ship since 2am (AEST) on Friday.
Mr Ritter said the workers’ detention had come as a shock.
“It’s a well-established principle that you can sail peacefully through international waters without having a nation state send its security forces to board your ship and arrest your crew at gunpoint,” he told AAP.
A DFAT spokesman said Australia was seeking “further information from Russian authorities to ensure the welfare of the Australian citizen and the permanent resident”.
Greenpeace said Gazprom - the world’s largest gas company - intends to start production from the Prirazlomnaya platform in 2014 and Greenpeace argues that the old oil platform is “an Arctic disaster waiting to happen”.
Gazprom has expanded its oil production operations in recent years and describes the oil field that the Prirazlomnaya will tap as an essential element of its oil business development strategy.