Italian prosecutors ordered the stricken Norman Atlantic ferry to be towed to the port of Brindisi on Tuesday as part of a criminal investigation, while Greek prosecutors also launched a probe into the cause of the fatal blaze.
One person was reported killed early in the rescue and salvage operation, and a further 10 bodies were recovered in the ensuing hours.
On Tuesday, two sailors from Albania were also killed as they were working to attach a towrope to the ferry. The incident brought the total provisional confirmed death toll from the disaster to 13.
"Given the ship was indisputably carrying illegal migrants who were probably hidden in the hold, we fear that we'll find more dead people once we recover the wreck," said Giuseppe Volpe, a public prosecutor in the Italian city of Bari.
Confusion over passenger list
There was uncertainty surrounding the number of people who were aboard the ferry when the fire broke out. According to the passenger list there were 478 people, but dozens of those have not been accounted for. Confusion also remained over how many people aboard had been attempting to immigrate illegally and thus had not been recorded.
The Italian-flagged Norman Atlantic, which had been chartered by Greek ferry operator ANEK Lines, was sailing from Patras in Greece to the Italian port of Ancona when the blaze broke out in the ship's garage early on Sunday.
Rescue helicopters and vessels from Italy and Greece spent 36 hours battling rough seas and high winds to winch hundreds of survivors off the ferry's upper deck.
Passengers report chaotic reaction to fire
Also under scrutiny will be the ship's adherence to safety standards and the actions of the owners and crew, following reports from passengers about a lack of coordination in the early stages of the emergency.
Many have said that they were woken during the early-morning fire by other passengers or by the smoke, not by alarms or the crew. A German passenger, Ute Kilger, described witnessing a middle-aged man barge past women, children and elderly people to be winched to safety before them.
"He just went and sat in the basket, which was clearly designed for children. I didn't know whether to laugh or cry," she was quoted as saying by news agency AFP, citing Italian media.
Greek passenger Uriana Thireou told AFP from a hotel in Brindisi that she had waited 23 hours for her rescue amid widespread panic.
"There were crew members around, but even they were panicked [because] it was impossible to organize so many people," Thireou said.
se/ksb (AP, AFP, dpa, Reuters)