An Italian court has in a landmark trial slapped a one-year jail term on the ship captain who returned 101 migrants rescued at sea to crisis-hit Libya.

In the first trial of its kind in Italy, the captain of the Italian-flagged Asso 28 was found guilty of violating international laws that forbid the forced return of people to countries where they or their rights are at risk.

Libya is not considered a port of safety under international law. The captain was sentenced to one year in jail, according to a copy of the court's ruling seen by AFP Friday.

The verdict, first reported by the Avvenire newspaper, was hailed by human rights organisations, with Doctors Without Borders (MSF) calling it "an important first step".

"But (it is) not enough: we need a radical change in the policies of Italy and Europe to immediately stop interceptions at sea and the system of forced returns," it said.

The ship picked up the migrants near an oil and gas rig in international waters and handed them over to the Libyan coastguard at the port of Tripoli, according to prosecutors in Naples.

The rescue took place on July 30, 2018, near the Sabratha platform which is operated by Mellitah Oil & Gas, a consortium of Libya's National Oil Corporation and Italy's ENI.

Among those pulled from the unseaworthy dinghy were five minors and five pregnant women.

Migrants sit on the ground after being recaptured by Libyan security forces following an escape attempt Migrants sit on the ground after being recaptured by Libyan security forces following an escape attempt Photo: AFP / Hussam AHMED

Despite the rescue taking place on an Italian-flagged ship which was under Rome's jurisdiction, no call was made to Italy's Maritime Rescue Coordination Centre (MRCC).

The Augusta Offshore company which owns the Asso 28 said at the time that the rescue had been coordinated by the "Marine department of Sabratha" and a Libyan coastguard officer who had boarded the ship.

Eni said it had been coordinated by the Libyan coastguard.

Italian prosecutors found no trace of a Marine department of Sabratha, or evidence that the Libyan MRCC had been alerted.

The verdict raised eyebrows among migrant rights experts in Italy, who argue that the court has essentially found illegal a practice encouraged and funded by Italy and the European Union.

Italy and the EU have for years been financing, training and providing aid to Libya's coastguard to stop, intercept and return asylum seekers under a deal severely criticised by human rights groups.

The verdict "interrupts a period of impunity, a Wild West situation in the Mediterranean", where confusion often reigns over which authorities are responsible for migrants, Avvenire's Nello Scavo, who has written extensively on the subject, told AFP.

But Sergio Scandura from Radio Radicale, whose tracking of the ship's movements was included in the prosecution's case, said there was "nothing to celebrate" because the trial failed to hold to account those who gave the captain his orders.

"Italy creates a criminal system... which illegally returns people to Libya. While the Italian legal system convicts a captain, rather than those who set up the system," said Scandura.