The United Nations High Commission for Refugees (UNHCR) said on Sunday that several shipwrecks had taken place over the weekend as migrants tried to cross the Mediterranean in their flimsy boats.

Nearly 600 were missing in boat capsizes that happened on Wednesday and Thursday last week, the UNHCR’s spokeswoman, Carlotta Sami, told journalists.

One of the boats, according to Sami, was carrying about 670 people. It did not have an engine and was being towed by another smuggling boat before it drowned. 25 people from the vessel managed to reach the towing boat and survived the tragedy. In another shipwreck on Friday, 45 people died and 135 migrants were rescued.

Survivors were being taken to Taranto and Pozallo in Italy, Sami said, adding that her agency was trying to gather information on the arrivals.

Rights group reports refugee deaths

Humanitarian organization Save the Children also reported three separate instances of boat capsizing in the last few days. Numerous asylum seekers who had survived the ordeal corroborated the reports, saying that the boat started to fill with water, forcing the captain of the tugboat that was towing the vessel to cut the towing line.

According to the Italian coastguard and the UN, 14,000 people were saved during operations in the Mediterranean last week. It remains unclear, however, how many people drowned in bids to reach Europe over the same period. The Italian navy confirmed that it pulled out 45 bodies overnight.

“It’s obvious that no matter the great effort made by rescuers, when the numbers are as high as we’re seeing this week, it’s very risky,” said Federico Fossi, a spokesman for the United Nations High Commissioner for Refugees (UNHCR) in Rome.