The tanker, owned by a Greek company and flying the Liberian flag, had 19 crewmembers aboard when it was attacked on its way from Romania to the United Arab Emirates on September 27.
A spokesman for the Greek Ministry of Merchant Marine and Island Policy has failed either to confirm or to deny the news.
"We know nothing about it," the spokesman said by telephone.
Fifteen vessels and a yacht currently remain to be kept by pirates, Sovfracht said.
The UN Security Council adopted on Thursday a resolution proposed by Britain introducing tougher sanctions against Somalia over the country's failure to prevent a surge in sea piracy.
Russia announced on Thursday it would deploy its warships off the coast of East Africa on a regular basis to prevent pirate attacks on merchant ships.