ROME (AP) — Seventeen Nigerian survivors of a 2017 migrant boat sinking have filed a case with the European Court of Human Rights accusing Italy of violating their human rights by “subcontracting” their rescue to Libya.

The case, backed by legal and human rights organizations, poses a direct challenge to Italy’s much-touted 2017 deal with Libya that has greatly reduced the number of asylum-seekers reaching Europe.

Those backing the case told a press conference Tuesday that the policy, which involved using EU funds to train and equip the Libyan coast guard to patrol its coasts and bring migrants back, had subjected would-be refugees to slavery, torture and other degrading and inhuman treatment once back in Libya.

They argue that Italy was responsible for the abuses because it maintained “effective control” over the Libyan rescuers via its own coast guard coordination center in Rome and an Italian Navy vessel docked off Tripoli that coordinates rescues locally.

And they said Italy was liable for the abuses because the violent conditions of Libyan detention centers where the migrants were held after their return were well-known and well-documented.

A call and email to the Italian foreign ministry seeking comment weren’t immediately returned.

But Italy has defended its support of the Libyan coast guard and held up as a success its 2017 agreement with the UN-backed Prime Minister, Fayez Serraj. Italian officials say it has saved lives and slowed to a trickle the number of migrants who risk their lives paying Libyan-based smugglers to ferry them to Europe aboard flimsy dinghies.

The policy has worked: 6,731 migrants have arrived in Italy so far from Libya in 2018, 84 percent down from 2017 and 78 percent down from the year before, according to interior ministry figures.

But human rights groups say that under its policy, Italy is shirking its international responsibilities to rescue migrants at sea and bring them to safety.

The case concerns the Nov. 6 sinking of a dinghy carrying 130 migrants, most of them Nigerian, off the coast of Libya. The Libyan coast guard — aboard the Italian-provided Ras Jadir vessel — arrived at the scene first but the German aid group Sea Watch 3 also responded with dinghies and rescued some 59 people. An estimated 20 people drowned.

Two of the 17 Nigerians who filed the case to the Strasbourg court May 3 were rescued by the Ras Jadir and were brought back to Libya, where they reported being tortured and suffering other rights violations, said Loredana Leo of the Italian non-profit Association for Juridical Studies on Immigration, who is representing the migrants.

They are now back in Nigeria, after having agreed to be repatriated to escape the Libyan detention centers, she said.

Another lawyer, Violeta Moreno-Lax of the Global Legal Action Network, said the case builds on the 2012 decision by the Strasbourg court that found Italy’s earlier “pushback” policy with strongman Moammar Gadhafi, also intended to stem migration by returning migrants to Libya, violated international law.

Moreno-Lax said Italy is committing the same violations “by proxy” with its new Libyan “pullback” policy.

The consortium is asking the court to rule that Italy has again violated international law and force it to award the migrants “moral reparations.” Lawyers said it would likely be two to three years before a decision is reached.