At least 30 African migrants drowned when their boat capsized off Yemen this week with reports of gunfire being used against those on board, the United Nations said Friday. At least 152 Somalis and Ethiopians were aboard the overcrowded vessel which left Aden in southern Yemen on Tuesday, the UN refugee and migration agencies said in a joint statement. "The vessel is believed to have been operated by unscrupulous smugglers who were attempting to take refugees and migrants to Djibouti, while also trying to extort more money from these refugees and migrants," according to the statement. The boat turned back and "capsized amid reports of gunfire being used against the passengers", it said. 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 last year. "There’s a flourishing trade, there’s no question," he told a regular UN briefing in Geneva. "There’s also an enormous trafficking industry within Yemen - people still heading further on into the Gulf states for work. That’s the reason why many of them are in Yemen at all." Millman doubted there were large numbers leaving Yemen by boat because most people who were stuck there did not have the means to get away. However, the empty boats making the 240-kilometer return journey clearly created opportunities to ferry people to Africa.