The International Organization for Migration, which is affiliated with the United Nations, says that since the start of 2014, almost 13,000 people have died trying to cross the Mediterranean. The United Nations also reported this month that the sea journey is now deadlier than at any point since the peak of the European migration crisis in 2015, even as unauthorized migration along the route has fallen to its lowest level in the same period.

In this latest deadly crossing, two rubber boats left the Libyan coast together in the early hours of Sept. 1, filled to bursting with hundreds of migrants. The engine of one boat failed, leaving it adrift, while the other began deflating around midday, Doctors Without Borders said based on survivors’ accounts.

The passengers used a satellite phone to send a desperate SOS as people began slipping from the shrinking boat into the water. The Italian Maritime Rescue Coordination Center “received an alert regarding the event and informed the search and rescue authority with jurisdiction over that area of the sea,” the Coast Guard said.

One survivor told Doctors Without Borders that the migrants could not swim, and that only a few had life jackets. The migrant said that the boat that sank carried 185 people, including 20 children, and only 55 had survived, indicating a death toll of 130, the aid group said. It said that other passengers were less precise but agreed that more than 100 people were missing and feared dead.

The International Organization for Migration said the Libyan authorities had reported only two bodies found and 25 people missing.

The number of people from the Middle East and Africa trying to reach safety and economic opportunity in Europe surged in 2015 and 2016, largely driven by the war in Syria. It has subsided since then, but how to handle those already in Europe, and those seeking to come, remains a political flash point across the continent.