EU policymakers are guilty of "killing by neglect" by cutting rescue missions in the Mediterranean – potentially costing the lives of more than 1,500 migrants, according to a report.
The Italy-led search and rescue mission, Mare Nostrum, ended in October 2014 and was replaced by Triton, which deployed fewer ships and prioritised deterring migrants over rescue operations, the report says.
Charities and UN officials warned the move could have a disastrous impact and lead to far more deaths at sea.
Documents unearthed by British universities showed the European border force Frontex pushed ahead with the change despite an internal assessment warning that if it was not properly planned it "would likely result in a higher number of fatalities".
The subsequent scaling back of search and rescue operations during the growing migrant crisis "created the conditions that led to massive loss of life", the damning report states.
Over 1,500 migrants died trying to cross the sea in the months after the change was implemented, according to the report, Death By Rescue: The Lethal Effects Of The EU's Policies Of Non-assistance At Sea.
Charles Heller, from Goldsmiths, University of London, co-author of the report, said policymakers were guilty of "institutionalised wilful neglect".
He told the Press Association: "Can we really qualify the ending of Mare Nostrum and its replacement by Triton in all knowledge of the consequences this would have, as a mistake?
"I would rather argue that this was a case of institutionalised wilful neglect, and that European policymakers and Frontex have made themselves guilty of killing by omission.
"Simply arguing that it was a mistake is insufficient. And if, as we show, policymakers and European agencies decided to disregard the risk their policy would entail for migrants, they should be held accountable for that negligence."
The report found European policymakers came to regard Mare Nostrum as a "pull factor" which encouraged migrants to make the perilous crossing because they knew they would be rescued if they got into difficulty.
It was scrapped in October 2014 and replaced by Triton, which deployed fewer vessels, patrolled an area further away from the Libyan coast where many migrants got into trouble, and did not have rescue as its operational priority.
But as the conflicts in Syria and Libya deepened, migrants continued to resort to people smugglers who packed them on to dinghies and sent them across the sea.
The number of migrants crossing the Med in the first four months of 2014 and 2015 stayed the same at 26,000, but death rates soared.
Sixty died in the first four months in 2014, but 1,687 died in the same four months the following year, meaning the chances of dying at sea increased 30-fold.
Charities warned the change could cost lives while Francois Crepeau, the UN rapporteur on migrant rights, said it amounted to saying "let them die because this is good deterrence".
The report said Frontex's planning of Triton "deliberately disregarded not only the external criticism of human rights advocates, but also its own internal assessment predicting increased deaths at sea".
Frontex prioritised stopping illegal border crossings and "deterrence took precedence over humans lives", it found.
By scaling down its search and rescue efforts, Europe effectively shifted the burden on to large merchant ships that were ill-equipped to cope.
Within a single week in April 2015 two ships capsized, killing around 1,200 migrants on board.
Reconstructing the shipwrecks using advanced spatial techniques, researchers found many died during and partly through the rescue operation itself because the merchant ships were not designed to deal with the disasters.
It stated that "EU policymakers and agencies carry a strong degree of responsibility for these deaths" which were, in effect, "death by privatised rescue".
Mr Heller said: "EU policymakers decided in 2014, in all knowledge of the deadly consequences, to end Mare Nostrum and replace it with the more limited Triton.
"It may not have been so much that Frontex and European policymakers were counting on more deaths as a deterrent.
"What is absolutely sure is that their priority was to make the conditions of crossing more difficult for migrants and for smugglers to act as a deterrent. And this priority was given precedent over migrants' lives."
He said Europe must ask itself if it can accept the deaths of thousands of migrants in the Mediterranean every year as a price worth paying to attempt to deter them, and called for an investigation into why the policy was taken up and not abandoned when the death toll began to rise.