The Greenpeace ship Arctic Sunrise, which was seized by Russian troops during an Arctic protest has docked in Murmansk .

Thirty activists, including four Russians, were being held on board the vessel.

Russia's Investigative Committee said the crew will be charged with piracy, which carries a sentence of up to 15 years.

"When a foreign vessel full of electronic technical equipment of unknown purpose and a group of people calling themselves members of an environmental rights organisation try nothing less than to take a drilling platform by storm, logical doubts arise about their intentions," Investigative Committee spokesman Vladimir Markin said.

The Dutch-flagged icebreaker had been monitoring the activities of Russian energy giant Gazprom.

The Arctic is generating growing interest from energy firms as global warming breaks up ice and reveals potentially vast oil and gas reserves.

But Greenpeace believes the energy firms have no plan in place to deal with oil spills in a previously unexplored environment.

The Arctic Sunrise was stormed by Federal Security Service agents during a helicopter raid on Thursday. It was in international waters at the time.

"Our activists did nothing to warrant the reaction from the Russian authorities," said Greenpeace director Kumi Naidoo.

Activists from Finland and Switzerland had climbed Gazprom's Barents Sea platform on August 18 to protest against oil drilling.

The two were detained after warning shots were fired.

They and the entire crew were then arrested and locked in the vessel's mess room.