At least 139 migrants, including 15 children, died after a boat carrying 305 people capsized off Djibouti, the United Nations’ International Organization for Migration (IOM) said Sunday. At least 84 people remained missing, while more than 80 survived, according to the agency.

The boat was traveling from Djibouti toward Yemen when it overturned near Guhere, north of Obock, on the evening of Oct. 8, the IOM said. The agency’s chief of mission in Djibouti, Alexandre Coissac, told The Associated Press that overcrowding was the main cause of the sinking.

The official death toll counts victims whose bodies were buried by Djiboutian authorities. Coissac told the AP that other victims were buried by fellow migrants and would not be included in the count unless their bodies could be verified. The final toll could therefore increase.

The IOM said all survivors were Ethiopian nationals. They were taken to a rescue center in Obock, where they received medical treatment and psychological support, according to the AP.

The route across the Red Sea from the Horn of Africa toward the Arabian Peninsula is used by migrants seeking employment in Gulf countries. The IOM reported that more than 900 migrants died or went missing along the route last year.

IOM Director General Amy Pope called for governments and donors to support safe and legal migration pathways. The agency’s account and the survivor and casualty figures were reported Sunday; the incident occurred Oct. 8.