Russia has underlined its determination to prosecute Greenpeace activists who boarded an drilling platform by declaring they posed a "real threat".
The state Investigative Committee's statement follows the raid on the offshore drilling platform in the Arctic last week.
All 30 people on the Greenpeace ship, including two journalists, have been jailed for two months pending the investigation.
The Investigative Committee said charges would be filed soon, but did not specify whether it is still considering charging the activists with piracy, a crime punishable by up to 15 years in prison.
The investigators said they are continuing to search the Greenpeace ship, the Arctic Sunrise, and have seized some equipment and documents.
The investigators said the Arctic Sunrise had violated the 500-meter security zone around the platform and that it was carrying equipment whose purpose was still unclear.
Greenpeace Russia denied it had entered the zone, established by Russian and international law. The inflatable boats used by activists to scale the offshore platform did violate this zone, but posed no danger, the organisation said.