Six migrants drowned and 13 went missing on Thursday when smugglers forced 180 Ethiopian migrants off a boat bound for Yemen, a day after a similar incident left 50 dead, the International Organisation for Migration said.
Survivors managed to make their way to Shabwa province, along Yemen's Arabian Sea coastline, which is now under the control of Yemeni troops backed by the United States.
An IOM spokesperson in Yemen told AFP the majority of the Ethiopian migrants appeared to be teenagers and young adults. 
The war in Yemen has left over 8,300 people dead and displaced millions since March 2015, but the country continues to draw migrants from the Horn of Africa seeking work in the prosperous Gulf countries further north. 
On Wednesday, human traffickers also forced more than 120 Somali and Ethiopian migrants into rough seas off Yemen to avoid arrest by local authorities, leaving at least 50 dead and 22 missing, the IOM said. 
IOM teams, working with the International Committee of the Red Cross, found the bodies of 29 migrants in shallow graves along the Shabwa coast. They had been buried by survivors.
The average age of those on board was 16. 
"The smugglers deliberately pushed the migrants into the waters since they feared that they would be arrested by the authorities once they reach the shore," an IOM emergency officer in Aden told AFP.
Laurent de Boeck, the IOM Yemen Chief of Mission, said the boat's crew immediately returned to Somalia to pick up more migrants to bring to Yemen on the same route.
"The suffering of migrants on this migration route is enormous. Too many young people pay smugglers with the false hope of a better future," he said. 
Long the poorest Arab country, Yemen is suffering from what the United Nations has labelled the "largest humanitarian crisis in the world". 
On top of years of fighting between the Saudi-backed government and Houthi rebels allied with Iran, the country is witnessing a cholera outbreak that has killed almost 2,000 people and a looming famine.
The IOM estimates some 55,000 migrants have nonetheless left the Horn of Africa for Yemen since the start of 2017, more than half of them under the age of 18.
It says the journey is particularly dangerous at this time of year due to high winds in the Indian Ocean. 
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