The European Union's official watchdog has opened an inquiry into the role of its Frontex border agency in a shipwreck off Greece last month in which hundreds of people died.
Migrant crossings in unseaworthy boats organised by human traffickers from northern Africa have increased significantly this year, with major loss of life.
EU Ombudsman Emily O’Reilly said she wants her investigation to make clear to the public "who is accountable for these deaths" as Frontex has unclear jurisdiction and limits to its authority over member states such as Greece when it comes to addressing the needs of those in distress at sea.
Key questions raised by the tragedy in the Mediterranean Sea include to what extent Frontex could have been more involved in the rescue, what exactly did it communicate to the Greek authorities, and what level of responsibility, if any, the EU agency has for the shipwreck.
Ms O’Reilly said: "A tragedy of this magnitude requires all those involved to reflect on their responsibilities and to be clear to the public who is accountable for these deaths."
As many as 750 people may have been on board the migrant ship that sank on 14 June.
So far, 82 bodies have been recovered and hundreds are still missing. Just over 100 survived.
Greece has been widely criticised for not trying to save the migrants before the sinking in international waters.
Officials in Athens say the passengers refused any help and insisted on proceeding to Italy, adding that it would have been too dangerous to try to evacuate hundreds of unwilling people from an overcrowded ship.
The ombudsman’s inquiry comes on top of Greek authorities looking into the responsibilities of their own coastguard in the tragedy.
Ms O’Reilly said: "It has been reported that in this instance Frontex alerted the Greek authorities to the ship’s presence and offered assistance but it is not clear what else it could or should have done."
Any new analysis coming out of the investigation could help those adrift in the Mediterranean Sea in the future, she added.
Frontex said that it planned to cooperate fully with the investigation, and clarified its role in any search and rescue mission.
"Frontex does not coordinate search and rescue operations. This is the responsibility of the national rescue coordination centres," it said.
"Nevertheless, Frontex sees the rescue of lives at sea as one of its essential roles and provides all the necessary support to national authorities when needed.
"This means that Frontex vessels conduct search and rescue operations when called upon."
