Nigerian migrants who survived a deadly sea crossing last year filed a lawsuit against Italy for violating their rights by supporting Libya’s efforts to return them to North Africa, their lawyers said on Tuesday.

Seventeen plaintiffs petitioned the European Court of Human Rights last week, Violeta Moreno-Lax, a legal advisor for the Global Legal Action Network, told reporters. She was among four lawyers and several humanitarian groups involved in the case.

The migrants say Italy violated multiple articles of the European Convention on Human Rights, including that people not be subjected to torture, held in slavery, or have their lives put in danger.

The United Nations, rights groups and news organisations say migrants face these conditions in Libya.

This is the first lawsuit to be filed against Italy for its decision to back the Libyan Coast Guard. The country lost a case in the same court in 2012 for directly handing over migrants intercepted at sea to Libyan authorities.

The legal process can take up to three years but should the migrants win they can be awarded damages, and Italy would be forced to abandon its policy of equipping, training and coordinating the Libyan Coast Guard, Moreno-Lax said.

"Using the Libyan Coast Guard as a proxy to turn back migrant boats is just a new way of camouflaging (Italy’s) strategy of fighting irregular migration in the Mediterranean by trapping them in what the Italian Foreign Ministry itself has qualified as ‘the hell’ of Libya,” Moreno-Lax said.