Smugglers forced more than 120 migrants from Ethiopia and Somalia - majority teenagers - off of a boat near the coast of Yemen on Wednesday, the International Organization for Migration announced in a statement.
The International Organization for Migration statement calls the incident "shocking and inhumane".
The staff aided 27 migrants on shore and found 29 shallow graves dug by survivors.
The Chief of Mission in Yemen Laurent de Boeck said his colleagues were told by survivors that the smuggler pushed them into the sea when he saw authorities. Yemen is now going through a conflict and humanitarian crisis but the migrants go there to try to reach Europe or the Gulf states. The agency says 22 migrants are missing. The migrants usually make the unsafe journey across the Mediterranean Sea with smugglers, who sometimes overcrowd the boats. Most of the people on the boat were from Ethiopia and Somalia. "Too many young people pay smugglers with the false hope of a better future", continued de Boeck.
"The approximate average age of the passengers on the boat was 16", the migration agency said.More news: Ex-defender sends urgent message to Arsene Wenger about Arsenal signings
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Despite the fighting in Yemen, African migrants continue to arrive in the war-torn country where there is no central authority to prevent them from traveling onward. With many still unaccounted for, the IOM believes up to 50 may have died.
The IOM estimates that around 55,000 migrants have left the Horn of Africa for Yemen since January.
Then they "simply went back to where they came from to pick more migrants and try to smuggle them into Yemen, again".
Some Somalis are desperate to avoid years of chaos at home with attacks by homegrown extremist group al-Shabab and deadly drought.
More than 111,500 people landed on the country's shores past year, up from about 100,000 in 2015, according to the Regional Mixed Migration Secretariat, a grouping of global agencies that monitors such movements in the area.