The Interfax news agency, quoting Russia's top investigator, said that it was possible a freighter embroiled in a high-seas mystery was carrying more than just timber.
The reported comment by Investigative Committee Chief Alexander Bastrykin is the first suggestion by a Russian official that the Arctic Sea could have been carrying a sensitive cargo.
The ship left Finland last month carrying timber, then seemed to vanish. Russia's defense minister announced last week that the ship had been found off West Africa and had been hijacked.
The developments raised suspicions the ship could have been carrying a secret cargo.
Interfax quoted Bastrykin on Tuesday as saying "we do not rule out the possibility that they might have been carrying not only timber."