Russia is moving detained Greenpeace activists from the northern port of Murmansk to an unknown location, most probably St Petersburg, which is about 1,500km away, according to the latest reports.
The 28 Greenpeace activists had been arrested in September when they tried to scale a Gazprom oil platform in the Pechora Sea, in protest against the Russian firm's Arctic oil exploration.
Russian authorities charged the activists and two reporters in the group first with piracy and then with hooliganism even as their detention triggered protests internationally.
A Greenpeace spokesperson said the activists left their detention centre at 5:00am (1200 AEDT) on Monday and were on a train, adding that sources in diplomatic channels said they were being moved to St Petersburg, news agencies reported.
The Greenpeace protest at the Gazprom oil rig was part of the global environmental campaign against Russia's decision to explore the offshore fields in the Arctic. The protesters said Gazprom, the Russian state-controlled energy company, had set up the world's first ice-resistant oil platform that would pose serious environmental hazard in the event of an oil spill.
An oil spill in the Arctic could destroy the Arctic life as the oil takes forever to be cleaned up in low temperatures because of the absence of bacteria that absorb the hydrocarbons, said Igor Chestin, chief executive of the environmental group WWF Russia.
"If you look at oil spills which happen in tropical waters, normally within a few years you don't find the oil anymore," Chestin said, adding that things would be different in the Arctic.
"... Not a single oil company currently has the technology to deal with an oil spill under the ice. Some of them know how to collect oil from the surface of the water, or from the surface of the ice, which is like land," he said.
The Greenpeace activists had sailed to the Barents Sea in their vessel Arctic Sunrise to stage a protest against the Gazprom project, with banners saying "Greed is killing the Arctic" flying on the deck.
On 18 September, they approached the Prirazlomnaya oil platform, a Gazprom project that Russian President Vladimir Putin considers as vital in the country's plan to boost oil output.
The campaigners' efforts to climb atop the rig was met with armed challenge from the Russian coast guard. The crew were arrested the next day and the ship was towed to the Murmansk port.
Russia stuck to its position that the protesters had violated the law by entering the restricted zone and had risked the safety of the rig and the workers there.
"A few boats approached the platform, and with the aid of special equipment, they tried to climb up the platform. They completely ignored the authorities' orders. Furthermore, if you recall, they rammed the coastguard ship," a spokesman of investigating team had said.
The Greenpeace has said their protest was peaceful.
Later, in October, Russian authorities said a search carried out in the vessel had revealed that the activists had possessed illegal drugs such as poppy straw and morphine, a claim the Greenpeace denied.
Russia initially said the activists were carrying out illegal research, but later charged them with piracy. Later the authorities changed the charge to hooliganism, a crime that attracts a maximum of seven years in prison under Russian law.