Spindler said the majority of the 357 survivors were Somalis, and 75 were Ethiopians.
Antonio Guterres, the UN high commissioner for refugees, said: "I am deeply saddened by this latest tragedy involving smugglers' boats carrying desperate people across the Gulf of Aden."
About half of the Somalian survivors said they were fleeing fighting between Ethiopian-backed Somali government forces and rival Islamic Courts fighters, Spindler said. UNHCR has asked neighbouring countries to be prepared to accept those fleeing.
Ali Mohamad Gedi. the Somali prime minister, swept into Mogadishu in an armed convoy on Friday after rival fighters fled the city they had ruled for six months.
More than 25,800 people have been recorded arriving in Yemen from Somalia this year, according to UNHCR. The boats from Somalia usually land along a remote stretch of tribal-ruled coastline.