Thirteen African migrants suffocated inside a shipping container while being transported over four days between two Libyan towns, a Red Crescent official has said.
Osama al-Fadly, head of the Red Crescent in Libya, said the deceased were among 69 migrants, many from Mali, who were packed into the container.
The locked container was transported from the central town of Bani Walid to Khoms in western Libya, from where the migrants were to be taken across the Mediterranean.
Instead, the traffickers unloaded the human cargo near an anti-trafficking force in Khoms on Tuesday. Mr al-Fadly said the deaths occurred on Monday.
Mr al-Fadly said many of the survivors had their limbs broken when they were thrown out of the container.
A five-year-old girl was among the survivors while two of the victims were aged 13 and 14, he said.
On its official Facebook page, the Red Crescent in Khoms posted pictures of the survivors, some of them with their arms in bandages, and with swollen eyes and bruises.
The tragedy is one of the latest in Libya, where human trafficking has thrived amid lawlessness in the north African country since the 2011 downfall of long-time dictator Muammar Gaddafi.
Competing governments based in eastern and western Libya rely on militias to maintain security and order. However, the militias gradually grew in number and weaponry and some have become involved in human trafficking.
Rights groups say migrants crossing Libya have been tortured, raped and subjected to forced labour. The number of migrants trying to cross the sea spikes and deaths become more frequent as summer gets nearer.
Earlier this week, dozens of migrants washed ashore at the western Libyan city of Zawiya after their rubber boat lost its engine. A survivor told the aid group that more than 100 people drowned in stormy weather.
The Libya-to-Italy smuggling route across the Mediterranean has seen record numbers of migrant drownings in 2016, Fabrice Leggeri, director of the European Border and Coast Guard Agency, said last week.
Some 4,579 migrant deaths were documented in 2016, up from 2,869 deaths the previous year and 3,161 in 2014. The real number of deaths is believed to be much higher.
More than 180,000 people made the crossing last year, an increase of 17% from 2015.