Mr Voitenko said it was nonsense to suggest pirates had been involved
A journalist has fled Russia after suggesting the Arctic Sea cargo ship that was apparently hijacked in July may have been carrying illegal weapons.
Mikhail Voitenko said he had been told to leave Moscow or face arrest.
The editor of Sovfracht, an online maritime journal, fled on Wednesday, saying he may not be able to return as his life would be in danger.
Eight men, mainly from Estonia, have been charged with hijacking and piracy over the case.
The men are suspected of seizing the ship and its 15-man Russian crew after raiding it disguised as police.
The alleged hijackers were taken to Russia after the ship was spotted 300 miles (480km) off the west coast of Africa on 16 August.
Mr Voitenko - who was among the first to cast doubt on official explanations about the ship's disappearance - told the BBC it was nonsense to suggest pirates had been involved.
Eight men have been charged with hijacking and piracy over the case
Instead he suggested the ship may have been carrying a secret shipment of weapons as part of a private business deal by state officials.
Speaking to the BBC from Turkey, Mr Voitenko said he had received a threatening phone call from "serious people" whom he suggested may have been members of Russia's intelligence agency, the FSB.
The caller told Mr Voitenko that those involved in the mysterious case of the Arctic Sea were very angry with him because he had spoken publicly, and were planning on taking action against him, he said.
"As long as I am out of Russia I feel safe," Mr Voitenko told the BBC. "At least they won't be able to get me back to Russia and convict [me]."
He also said Nato knew exactly what had happened to the Arctic Sea.
A Nato spokesman said the alliance had been in contact with Russia throughout the crisis, but would not say anything more.
The FSB refused to comment on the allegations.
Mystery continues to surround the ship's disappearance, amid speculation the ship may have been intercepted by Mossad - Israel's foreign intelligence service - in order to prevent a shipment of illegal arms to the Middle East.
There has been much speculation over what actually happened on the ship
The 4,000-tonne Maltese-flagged vessel vanished in July days after leaving Finland with an apparent cargo of timber worth $1.8m (£1.1m), destined for the Algerian port of Bejaia.
Observers have questioned why the alleged hijackers would risk seizing the Arctic Sea in one of Europe's busiest shipping lanes for a relatively inexpensive cargo.
Russian authorities said nothing suspicious was found aboard the ship when it was found last month, but have said a more thorough inspection would be carried out when the Arctic Sea arrives in the Russian port of Novorossiisk.