ROME — The Council of Europe is asking Italy to explain what its naval ships are doing off Libya’s coast amid concerns that Europe-bound migrants who are sent back to Libya face “a real risk” of torture or inhuman treatment.

In a Sept. 28 letter published Wednesday, the council’s human rights commissioner, Nils Muiznieks, warned Interior Minister Marco Minniti that Italy again risked violating the European Convention on Human Rights.

The convention prohibits exposing people to “torture or inhuman or degrading treatment or punishment.”

Italy announced in July it was sending naval units to Libya’s coast to help the local coast guard prevent migrants from leaving. The increased patrols, coupled with Italy-backed deals to use militias on land to prevent would-be refugees from leaving, has greatly reduced the migrant flow to Europe: To date, the number of migrants who reached Italy in 2017 is 25 percent less than 2016, according to Italian interior ministry data.

Aid groups, human rights organizations and media reports have documented the wretched conditions of Libyan detention centers, where physical and sexual abuse of migrants is rampant.

In the letter, Muiznieks recalled that the European Court of Human Rights in 2012 found that Italy had violated the treaty by returning migrants who were intercepted in international waters to Libya.