More than 100 migrants from Somalia and Ethiopia, including women and children, may have drowned while trying to reach Yemen, the UN refugee agency says.
Bossaso is at the centre of the people-trafficking route from Somalia
Migrants on other boats told the UNHCR that a vessel carrying 93 people sank and only the four crew survived.
It was one of six boats which set sail from the Somali town of Bossaso.
Such incidents are not uncommon in the Gulf of Aden. The UNHCR said it was appalled at this ongoing human tragedy.
The crew of another boat reportedly forced their 85 passengers to jump overboard before reaching land last week.
Of these, 18 drowned - 17 Somalis and one Ethiopian. Seven bodies have been recovered.
Somalis - fleeing anarchy in their homeland - and Ethiopians go to Yemen, before travelling on to Europe.
An unknown number of African migrants also drown each year in the Mediterranean Sea, trying to cross to Europe.
Some 535 people have arrived in Yemen in the past week.
They report that another 1,500 people are waiting in Bossaso to cross over to Yemen.
Bossaso is controlled by Puntland, a break-away Somali republic.