MILAN (AP) — Survivors say as many as 240 people have died in two shipwrecks off Libya, the U.N. refugee agency reported Thursday, bringing this year’s toll to more than 4,220 migrants dead or missing in risky Mediterranean Sea crossings, the highest count on record.

Carlotta Sami, a UNHCR spokeswoman in Italy, said 31 survivors of two shipwrecks who arrived on the southern Italian island of Lampedusa reported that the rubber dinghies they were travelling in had capsized Wednesday in heavy seas shortly after leaving Libya.

The first dinghy — which carried around 140 people, including six children and about 20 women, some pregnant — sank when wooden planks laid at the bottom broke, causing the dinghy to capsize 25 miles (40 kilometres) off the Libyan coast, the UNHCR said. Twenty-nine people were rescued, and 12 bodies were recovered.

In a separate operation, two women found swimming at sea told rescuers that 128 other people had died in their wreck.

UNHCR emphasized that the number of dead was an estimate.

International agencies rely heavily on survivor accounts to tally the number of people dead or missing in the dangerous journey across the Mediterranean in smugglers’ boats. Often the boats sink in high seas, where it is difficult if not impossible to recover any bodies.

In both cases reported Thursday, most people on board appeared to have been sub-Saharan Africans.

UNHCR said the increased number of deaths this year is partly due to the fact that smugglers are often using rubber dinghies, which are prone to deflating, capsizing and losing people who fall overboard. In addition, more migrants are arriving with severe burns from being exposed to fuel mixed with sea water in the bottom of the dinghies. Smugglers are using rubber dinghies because they are cheaper and easier to obtain.

According to the IOM, 3,777 people were dead or missing as they tried to cross the Mediterranean last year, the previous high.