At a summit in Malta, leaders of the bloc approved a new strategy to "break the business model" of traffickers who have helped more than half a million mainly African migrants enter the European Union via Libya and Italy in the last three years.
But non-governmental organizations have warned it could result in women and children being returned to inhumane conditions and left vulnerable to rape, beatings and forced labour as well as forcible repatriation to uncertain fates in their home countries.
"Sending children back to a country many have described as a living hell is not a solution," said Ester Asin of British charity Save the Children, ahead of the approval of the widely-trailed new EU strategy.
The cornerstone of the plan involves funding and training the Libyan coastguard to make it better able to intercept migrant boats before they reach international waters patrolled by an Italian-led search-and-rescue operation.
The EU leaders also welcomed a deal announced on Thursday under which Italy will help Libya's UN-backed government of National Accord to stem the migrant flow.
That bilateral accord includes controversial proposals to set up temporary camps to house illegal immigrants arriving in the north African state, pending their deportation or voluntary return to their home countries.
The camps would be Libyan-run but EU-funded with Italy providing medical support.
With Libya in a chaotic, conflict-scarred state and the UN-backed administration only in control of sections of the country's vast coastline, the prospect of turning boats back and establishing so-called "welcome centres" in the trouble country is causing deep concern in the humanitarian community.
Human Rights Watch said the EU would be flouting its international obligations by "outsourcing responsibility" for the migrants to one party to a conflict in a fundamentally unstable state.
As the EU leaders boarded a boat to cross Malta's historic harbour to their lunch venue, rescue ships off Libya were engaged in multiple frantic operations to save hundreds of people including babies from a fresh wave of rickety boats.
"It's an absolute nightmare in the Med right now," the Doctors with Borders (MSF) charity said.
'Shoot us like dogs'
Aboard The Aquarius, a humanitarian ship chartered by SOS Mediterranee and MSF, would-be refugees described the fear they have of being sent back to Libya and falling again into the arms of traffickers.
"The Libyans shoot us like dogs," Boubacar, a 17-year-old Guinean was quoted as saying by an SOS Mediterranee spokeswoman.
Emmanuel, from Cameroon, said a friend of his had twice experienced the terror of being returned to Libya at gunpoint after boarding a smuggler's boat for Italy.
"They take you to a prison, give you a phone and make you phone your family to get them to pay to get you out," he said.
The EU's attempts to get Libya to effectively blockade its own coastline follows a record year for arrivals in Italy (181,000 in 2016) and the deadliest winter yet in the Mediterranean, with migrants perishing at sea at a rate of 15 per day over the last three months, according to UN refugee agency (UNHCR) figures.
Rescuers say the death toll has risen because traffickers are sending more and more overcrowded, unseaworthy vessels to sea in tough winter conditions in order to maximize profits while they can.
Critics of EU efforts to resolve the crisis say the search-and-rescue operation in the international waters off Libya encourage traffickers because they know they only have to get their human cargo a few miles offshore and they will be picked up and taken to Italy.
But Rome maintains it has a moral duty to save lives.
The UN's children agency UNICEF said an unprecedented 1,354 migrants, including 190 children, had died in the Mediterranean in the past three months, most of them on the Libya-Italy route.