Greenpeace activists who scaled an oil platform to protest Arctic drilling could be charged with piracy, Russian investigators said Friday, as border guards began towing their ship to port.

Russian border guards stormed the ship from a helicopter late Thursday after Greenpeace activists scaled the platform, owned by state energy giant Gazprom, to protest plans to drill on the Arctic shelf.

Special forces armed with guns locked up the crew of about 30 people from Russia, the Netherlands, Finland, Switzerland and other countries and now control the ship, Greenpeace said.

Russia's powerful Investigative Committee said Friday border guards had seen evidence the crew may have committed piracy, which is carries a prison term of between five and 15 years in Russia.

"The Arctic Sunrise ship is being taken to the port of Murmansk," Greenpeace said on Twitter on Friday. Border guards said the journey to Murmansk, which lies 1,485 kilometres (920 miles) north of Moscow, would take three days.

Greenpeace is campaigning against surveying of oil and gas fields on the Arctic shelf, arguing that any oil leak would be catastrophic in the pristine environment and impossible to bring under control.

The federal security service (FSB), which oversees the border guards, and the Russian foreign ministry have accused the activist ship of endangering lives, infiltrating the platform and conducting "extremist" activities.

Greenpeace expert Roman Dolgov told RIA Novosti from onboard the ship: "We are facing quite serious accusations: of terrorism and carrying out illegal scientific research."

He said the activists were locked in the ship's mess but were allowed out to go to the toilet or smoke.

A senior FSB official said there was evidence the crew were conducting "illegal scientific research."

"Upon inspection of Arctic Sunrise, we found large quantities of electronic equipment... and there is evidence of possible... illegal scientific research," the head of FSB security services in Murmansk region, Mikhail Karpenko, told Rossiya24 television.

Carrying out illegal scientific research on the Arctic shelf under Russian law carries a maximum sentence of two years of community service.

Greenpeace said this was likely to be the only charge the authorities could use against the ship, because the oil platform is located in Russia's exclusive economic zone on the Arctic shelf, and most Russian laws do not apply there.

"Even if they have equipment on board, it doesn't mean they were using it illegally," added Mikhail Kreindlin of Greenpeace's Russian office.

Greenpeace said border guards on Wednesday had detained two activists, Sini Saarela from Finland and Marco Polo from Switzerland, who attempted to scale Gazprom's Prirazlomnaya oil platform, and took them on board their patrol boat.

The activists were later returned to the Arctic Sunrise and locked up with their crewmates, Greenpeace said.

Greenpeace said the Dutch-flagged Arctic Sunrise was in international waters at the time of the storm, in the southeastern part of the Barents Sea north of Norway and western Russia, which is sometimes called the Pechora Sea.

Russia's foreign ministry on Thursday called in the Dutch ambassador to Moscow to complain about the ship's "provocative" actions.

The prospect of more accessible energy riches as global warming gradually melts the sea ice is prompting rivalry between Russia, Norway and Canada to explore and exploit the region.

The Prirazlomnoye oil field is located 60 kilometres from shore and has estimated reserves of 72 million tonnes, according to Gazprom. The company announced this year that production will begin before the end of 2013.