The European Court of Human Rights has ruled that Italy violated the rights of Eritrean and Somali migrants by sending them back to Libya.
The 13 Eritreans and 11 Somalis were among a group of about 200 people who left Libya on three boats in 2009. Two of the 24 have since died.
The court ordered Italy to pay each migrant in the case 15,000 euros (£13,000; $20,000) in damages.
Last year Italy suspended a 2008 deal with Libya on sending migrants back.
The Grand Chamber judgment in the case of Hirsi Jamaa and Others v Italy found that the applicants had been exposed to the risk of ill-treatment in Libya and of repatriation to Somalia or Eritrea.
That was a violation of Article Three of the European Convention on Human Rights – prohibition of inhuman or degrading treatment.
There was also a violation of Article Four of Protocol Four – prohibition of collective expulsions, according to the judges’ unanimous ruling.
The Grand Chamber judgment is final, meaning it is legally binding on Italy.
The judgment was welcomed by the UN refugee agency (UNHCR), which called it “a turning point regarding state responsibilities and the management of mixed migration flows”.
The UNHCR had presented its position to the Strasbourg court, saying states had an obligation not to forcibly return people to countries where they faced persecution or serious harm.
The court said that in 2009 Italy conducted nine operations at sea to intercept migrant boats, in line with the bilateral deal signed by former Prime Minister Silvio Berlusconi and the late Libyan leader, Col Muammar Gaddafi.
On 26 February 2011 Italy announced that it was suspending the agreement because of the unrest in Libya.
In their plea to the court the migrants said the Italian authorities who shipped them back to Libya did not tell them where they were going or check their identities.
Once in Tripoli they were handed over to the Libyan authorities.
Effort to trace migrants
Thursday’s ruling came after the Italian Council for Refugees had argued that the migrants’ rights had been seriously breached, as they had been denied any chance to claim sanctuary in Italy.
According to the court, 14 of the migrants had been granted refugee status in 2009 by the UNHCR in Tripoli.
But the anti-Gaddafi uprising in 2011 disrupted contact between the applicants and their legal representatives.
The lawyers are currently in contact with six of the applicants, four of whom live in Benin, Malta or Switzerland and some of whom are awaiting a response to their request for international protection.
One applicant is in a refugee camp in Tunisia and is planning to return to Italy.
In June 2011 refugee status was granted to one of the applicants in Italy after he had clandestinely returned there.
The 2008 Italy-Libya deal amounted to an official apology from Italy to its former North African colony.
Italy agreed to pay $5bn in reparations in return for greater Libyan co-operation on stopping illegal migration.
Fewer migrants risked the perilous voyage as the interceptions at sea led to boatloads being sent back.
However, during the Arab uprisings in the first half of last year there was a sharp increase in the number of African migrants arriving in Italy in overcrowded boats.