The UN refugee agency raised concern on Friday over the record numbers of Ethiopians and Somalis flocking to Yemen, despite the deteriorating security situation there.
Last year 103,000 refugees, asylum seekers and migrants crossed the Gulf of Aden and Red Sea -- almost double the 2010 figure of 53,000. A reported 130 drowned.
Most arrive dehydrated and malnourished only to face physical and sexual attacks and trafficking, UN High Commissioner for Refugees spokesman Adrian Edwards said at a briefing in Geneva.
"Instability and the reduced police presence in Yemen are giving human traffickers and smugglers more room to operate," said Edwards, who said the situation was also hampering the activities of humanitarian teams.
Three Ethiopians were reportedly killed while trying to escape from smugglers in Taiz governorate on January 13, he said.
Somali refugees recently accounted for the majority of all arrivals in Yemen, but Ethiopian migrants have since become the largest group.
Somalis say conflict, insecurity, drought and famine are driving them out of their country, while Ethiopians cite a lack of economic opportunities and go to Yemen to try to reach other Gulf states.
They are regularly robbed and attacked by smugglers and traffickers who try to extort money from them.
Yemen, one of the world's poorest countries, has become increasingly unstable as militants exploit a central government weakened by months of protests against President Ali Abdullah Saleh.