A dog standing near a train believed to be transporting the 30 people arrested over the Greenpeace protest. Sergei Khitrov

Thirty people arrested in Russia over a protest against Arctic oil drilling were moved from the northern city of Murmansk on Monday on their way to pre-trial detention centers in St. Petersburg, federal investigators and Greenpeace said.

The transfer, which follows a reduction of the charges against 28 activists and two journalists, may be aimed at curbing international criticism of Russia over what the environmental group says was a peaceful protest.

Activists have reported being confined for 23 hours a day in bleak, sometimes ice-cold cells in Murmansk, a port city above the Arctic Circle whose remote location complicates access for lawyers and consular officials.

The Kremlin has rejected Greenpeace head Kumi Naidoo's offer to come to Russia and stand as security for the release of the detainees, who come from 18 nations on five continents.

The 30 were arrested after coast guards boarded the Greenpeace icebreaker, Arctic Sunrise, following a protest at an oil platform owned by state-controlled Gazprom off Russia's northern coast Sept. 18.

Now charged with hooliganism and facing up to seven years in prison if convicted, they had been denied bail and held in pre-trial detention in Murmansk, 1,030 kilometers north of St Petersburg.

Lawyers who tried to visit them Monday were told they had been moved out before dawn, Greenpeace said, and Russia's federal Investigative Committee said they would be taken to detention facilities in St. Petersburg.

"St Petersburg has some daylight in the winter months, unlike Murmansk," Ben Ayliffe, an Arctic campaigner for Greenpeace said in a statement, although he added there was no guarantee of better conditions.

When prisoners are transferred across Russia's vast distances, they are often taken in special trains.

"From the information we have, their [railroad] cars are not heated," Ayliffe said. "We have advised the 30 to dress in warm clothes and shoes. We have also organized prompt deliveries of additional supplies of warm outfits."

Russia says the environmental activists violated the law in the protest, in which some tried to scale the Prirazlomnaya platform, Russia's first offshore oil rig in the Arctic and part of its efforts to develop the region's oil and gas reserves.

Russia has refused to take part in a case at the International Tribunal for the Law of the Sea, in which the Netherlands is seeking the release of the activists, two of whom are Dutch, and the Dutch-registered Greenpeace vessel.

Greenpeace Activists Held in Russia Being Moved to St. Petersburg