Asylum seekers looking for shelter in Europe have been illegally forced to leave Italy and locked up in unofficial prisons at sea, an Al Jazeera investigation with Lighthouse Reports and other media partners reveals.

The joint investigation published this week uncovered evidence of an illicit practice known as “pushbacks” against adult refugees and migrants as well as children who were made to suffer inhumane conditions as they were transported from Italy to Greece.

Nationals from Afghanistan, Syria and Iraq described being detained without formal authorisation on board commercial ferries operating routes between the two countries over the past year.

They said they were held in dark metal boxes and small rooms without food or water, sometimes for more than a day, as they were shipped back to Greece after being caught trying to reach Italy’s Adriatic ports of Venice, Ancona, Bari and Brindisi.

One Afghan asylum seeker who was held inside a container, said his room was about 2 metres (6.5 feet) long and 1.2 metres (3.9 feet) wide.

“You have only a small bottle of water and no food at all. … We had to stay in that small room inside the ship and accept the difficulties,” the Afghan national said.