A spokesman for the Danish navy, which carried out the dramatic rescue, said it was not clear that the pirates had any idea how to navigate the Iranian vessel which they had been using as a mother ship.
“They were therefore using the crew as sort of slaves,” Kenneth Nielson told AFP, pointing out that the pirates had not demanded ransom for the crew members and had not tried to enrich themselves “on the hostage-taking itself.”
Sixteen of the crew were rescued on Sunday night in an operation by the Danish warship Absalon, part of a NATO-led counter-piracy mission. However two other hostages, one Iranian and one Pakistani, were killed in the rescue bid.
The navy has now launched an investigation into the operation, and acknowledged that the two casualties could have by killed by the Danes.
“We cannot rule out that we were the ones who caused the deaths,” Navy captain Steen Engelbrecht Pedersen told the Danish Ritzau news agency on Tuesday.
A Danish military prosecutor had opened an investigation to “shed light on what happened,” he added.
The Danish warship had been following the hijacked vessel for several days off the Somali coast, according to a Navy statement.
“When the pirates tried to leave the coast, Absalon intervened and stopped the mother ship, before it could pose a threat to shipping in the open sea.”
NATO meanwhile said the Absalon had approached the vessel “that had been previously captured by pirates and was being used as a mother-ship.”
“When warning shots were unsuccessful, small arms fire from … Absalon disabled and stopped the vessel. Shortly after, the vessel stopped and the suspected pirates were seen dropping their weapons overboard.”
Seventeen pirates had been taken into custody during the operation, according to NATO.