At least 30 African refugees and migrants drowned off the coast of Yemen this week in a boat operated by smugglers who are reported to have fired on passengers.
"There's a flourishing trade, there's no question", he told a regular United Nations briefing in Geneva.
The agency issued a statement Friday, saying the overcrowded boat had more than 150 Ethiopians and Somalis when it overturned just after leaving a port near Aden earlier this week.
Yemen has been embroiled in a civil war and a failing economy, leaving millions of people in starvation.
The statement said the agency and its partners were working to learn more about the episode and were providing emergency assistance to survivors.
Migrant drownings between Yemen and the Horn of Africa are recorded much less often than on the route between North Africa and Europe, but IOM spokesman Joel Millman said 87,000 people risked their lives to reach Yemen a year ago. At least 111 deaths were reported in 2017, and 109 in 2016. The boat packed with 152 Somalis and Ethiopians was operated by smugglers, who reportedly opened fire in an attempt to extort money from the passengers. About 100,000 migrants from Ethiopia left Saudi Arabia previous year, either voluntarily or through deportation, including some who returned via Yemen.
Yemen has been embroiled in a civil war pitting a Saudi-led coalition backing an internationally recognized government against Iran-backed Shiite rebels since March 2015. Millions of Yemenis are facing acute hunger and disease, including a cholera epidemic that has sickened roughly 1 million people. These conditions leave refugees and migrants more vulnerable to human rights violations, such as human trafficking.