Two Albanian seamen were killed on Tuesday during an operation to secure the stricken Italian ferry Norman Atlantic.

The seamen died after the cable between their tugboat and the ferry snapped as they were towing the fire-blackened vessel towards the Albanian port of Vlore.

“One man died on the spot when one cable broke after it got stuck in the propeller,” a port authority official in Vlore told Reuters. “The other died on board … when being assisted by a helicopter medical team.”

The latest deaths came after it emerged that prosecutors had made the ship’s owner and, more controversially, its captain, suspects in their inquiry into the disaster. The charges they are considering include multiple manslaughter, negligence leading to a shipwreck and negligence leading to bodily harm.

Captain Argilio Giacomazzi, who was the last person to abandon the fire-gutted ferry on Monday afternoon, has been hailed by many of his compatriots as a hero. His conduct was in stark contrast to that of the skipper of the Costa Concordia, the cruise liner that was wrecked off the coast of Tuscany in 2012, who abandoned ship long before the evacuation was complete.

The Norman Atlantic was on its way from Patras in Greece to Ancona in Italy on Sunday morning when a fire broke out on its car deck. The 26,900-ton roll-on, roll-off ferry was chartered to a Greek line, Anek, but Italian prosecutors have claimed jurisdiction over the inquiry on the grounds that the ship was flying the Italian flag.

Passengers have alleged that the alarm was sounded too late and that the crew were ill-prepared for the emergency. It is has also emerged that a malfunction of at least one fire door was among the defects noticed in an inspection of the vessel earlier this month.

Carlo Vicientini, the ship’s owner, said in a statement on Sunday night that the problem had been “immediately eliminated”. The commander-in-chief of the Italian coastguard, Admiral Nicola Carlone, told a press conference in Rome on Monday that the ship, which was launched only five years ago, was fully seaworthy.

Ten people aboard the Norman Atlantic are known to have died in the disaster but confusion continues to surround the number of missing.

Anek Lines said there were 475 people aboard the ferry. But according to Italian officials only 427 were rescued.

Even assuming that all of the dead are included in the operators’ tally, that leaves 38 people unaccounted for. On Monday evening, Admiral Giovanni Pettorino of the Italian navy said that 80 of those rescued were not on the list of passengers and crew. That would bring the total number of missing to 118.

Two of the 49 rescued passengers who came ashore at Bari on Monday were Afghans trying to reach Italy without authorisation.