Doctors Without Borders says that armed men threatened some 112 migrants trying to cross the Mediterranean, then sped away with women and children while dozens of men and boys jumped into the sea.
The humanitarian group’s boat, the Geo Barents, arrived at the scene in international waters off the Libyan coast on Thursday, rescuing 83 men and unaccompanied minors, 70 of whom were plucked from the sea.
No fatalities were reported.
Armed men on two speedboats, who identified themselves as Libyan coast guard, were spotted nearby.
One boat had taken on board 24 women and four children, and the Geo Barents crew were told that they would be handed over once the men had been rescued.
But the vessel then sped away, according to Doctors Without Borders.
It said that one of the rescued men, whose wife and children were taken away, claimed the armed men had fired into the air and into the water to stop the migrant vessel.
The man told his rescuers that the armed men took only women and children and had pushed him back when he tried to get onto their speedboat.
Doctors Without Borders, known by its French acronym MSF, appealed to all competent authorities and organizations to reunite the families, underlining that Libya was not a safe place.
It denounced Thursday’s aggression as “unacceptable”, saying it had put in danger the lives of many people, and separated families.
The United Nations reports that 2,124 migrants have died in the attempt to make the perilous Central Mediterranean crossing this year.