More than 100,000 migrants have made the dangerous crossing of the Mediterranean Sea to Europe so far this year, the United Nations said Tuesday, reporting a spike in arrivals that will add to Europe's migration concerns. Since January, 103,000 refugees and migrants have risked their lives—often on substandard boats—to reach Europe, the U.N. High Commissioner for Refugees (UNHCR) said. The refugee agency "is stepping up its presence in Greece and in southern Italy in response to the dramatic increase in numbers of refugees and migrants who we have been seeing arriving," UNHCR spokesman Adrian Edwards told reporters in Geneva. While the number of migrants arriving in Italy marks a 10 percent increase over the same period a year ago, the situation in Greece has worsened dramatically. At least 48,000 migrants have arrived in Greece so far this year, compared to 34,000 arrivals during all of 2014, according to the U.N. International Organization for Migration (IOM). Another 920 have arrived in Spain this year and 91 in Malta, according to the latest UNHCR statistics. Mass drownings in the Mediterranean have claimed almost 1,800 lives so far this year, the IOM said. About 800 died in a single sinking in April, marking the biggest maritime disaster in the Mediterranean since the second world war and prompting European governments to increase search-and-rescue operations.