A cargo ship that went missing for more than two weeks might have been carrying a more sensitive cargo than first declared, a Russian top investigator says.

Comments by Alexander Bastrykin published by Interfax news agency are the first official suggestions that the Arctic Sea was carrying more than timber, BBC reported.

The vessel was eventually found on August 16 off the West African coast, having apparently being hijacked.

There has been much speculation it may have been carrying weapons for export.

Eight people, mainly from Estonia, are still in custody in Russia on suspicion of hijacking the vessel.

The 4,000-tonne Maltese-flagged Arctic Sea set sail from Finland in July with a crew of 15, and was said to have been carrying timber worth $1.8 million.

"We do not rule out the possibility that [the Arctic Sea] might have been carrying not only timber," Bastrykin, the head of the investigative committee, was quoted as saying by Interfax on Tuesday.

"This is why we need to examine the vessel - so that there are no dark spots in this story."

The ship had been scheduled to dock in the Algerian port of Bejaia on August 4, but never arrived.

HSH/SC/AKM