Five French military personnel were charged on Thursday with non-assistance to persons in danger over the 2021 sinking of a migrant boat crossing the Channel to Britain, a judicial source said.
Authorities reportedly detained around a dozen people, including several military personnel deployed as coastguards in northern France, in the investigation into the tragedy.
Those charged included three women and two men on duty at the Channel rescue centre at the time, a source familiar with the matter said.
The sinking of the small boat in the Channel in November 2021 left 27 migrants dead, the worst such disaster in recent times.
The probe in France is focusing on allegations that French service personnel on duty in the north of the country failed to respond properly to the distress calls of those on board.
It is suspected that as many as 15 distress calls to the French authorities were not properly answered.
The victims aged between seven and 46 are believed to have boarded an unseaworthy boat on the French coast.
They also included Iranian Kurds, Ethiopians, Somalians, Afghans and Egyptians.
English Channel crossing tragedy - in pictures
A French border police unit arrested 15 people last year on suspicion of being part of a smuggling network that arranged places on the boat.
Another suspect, Harem Ahmed Abwbaker, is facing extradition proceedings in Britain.
The disaster sparked cross-Channel feuding as Britain and France blamed each other for the tragedy.
Britain cited the "dangerous and perilous conditions" in the Channel as justification for deporting asylum seekers to Rwanda to deter migration in small boats.
Another four people died and 43 were rescued when a boat capsized in the Channel last December.
A cooling of tensions with France led to a new deal this year for more patrols on French beaches in exchange for €541 million ($580.3 million) from Britain.
