Italian Prime Minister Giorgia Meloni has been placed under investigation over a government decision to release a Libyan police officer wanted by the International Criminal Court (ICC).

Osama Elmasry Njeem is suspected of crimes against humanity including murder, torture, rape and sexual violence as a prison overseer in Tripoli.

Migrants expressed their dismay and sense of betrayal on Wednesday over Italy's decision last week to release a Libyan policeman wanted by the International Criminal Court (ICC) for war crimes and human rights abuses and allow him to return home.

Italy's prime minister took to social media on Tuesday to announced that she is being investigated but sounded a defiant note: "I cannot be blackmailed," Giorgia Meloni said. "I will not let myself be intimidated.