The Investigative Committee said that the detainees' refusal to testify has impeded the investigation. "That prompts the investigators to thoroughly check all possible versions, including the seizure of the platform for financial benefit, terrorist motives, the conduct of illegal scientific research and espionage," the agency added.
It dismissed the Greenpeace claim that the protest was peaceful, saying it was a crime under an international law to try to seize an oil rig.
Vladimir Chuprov of Greenpeace Russia said the activists "are no more hooligans than they were pirates" and should be freed immediately.
"We will contest the trumped-up charge of hooliganism as strongly as we contested the piracy allegations. They are both fantasy charges that bear no relation to reality," he said in a statement.
Chuprov also dismissed the committee's warning that it may charge some of the activists with use of force against officials, pointing at Greenpeace's 42-year history of peaceful protest.
"They arrived at that oil rig in a ship painted with a dove and a rainbow," he said. "Those brave men and women went to the Arctic armed with nothing more than a desire to shine a light on a reckless business. "
The platform is the first offshore rig in the Arctic. It was deployed to the vast Prirazlomnoye oil field in the Pechora Sea in 2011, but its launch has been delayed by technological challenges. Gazprom said in September that it was to start pumping oil this year, but no date has been set.
The Netherlands has asked the International Tribunal for the Law of the Sea to order Russia to release a Greenpeace protest ship and the activists who were on board.