The migrants and asylum seekers chiefly come from countries in sub-Saharan Africa, particularly Somalia and Eritrea, it said. Others originate from Syria, Egypt or Pakistan, and smaller numbers from Gambia, Mali and Afghanistan.
The U.N. refugee agency recorded some 40 deaths in the first six months of 2013, a figure based on interviews with survivors of the crossing.
For 2012 as a whole, some 15,000 migrants and asylum-seekers reached Italy and Malta -- and almost 500 people were reported dead or missing at sea, it said.
The U.N. agency credits the efforts of the Italian coast guard and Maltese armed forces for a reduction in migrant deaths in the first half of 2013 compared with the previous year.