At least 1,000 migrants died in shipwrecks and boat capsizings in the central Mediterranean Sea last week, the International Organization for Migration (IOM) estimated on Tuesday.
Earlier in the day, UN Refugee Agency (UNHCR) updated its death toll to 880 people, based on new information from survivors and additional accidents.
Last week, Italian authorities coordinated dozens of rescue operations on the Libya-Italy sea route, saving about 13,000 people.
There were also at least three shipwrecks, on Wednesday, Thursday and Friday, and at least 50 bodies were recovered.
Taking into account missing persons' reports from survivors, about 500 died on Thursday, 200-250 on Wednesday and another 200-250 on Friday, and 47-48 are missing from another accident, Flavio Di Giacomo, an IOM spokesman in Rome, told dpa.
"If we add these numbers up, we are well above 1,000," he said.
UNHCR spokesman William Spindler said his agency learned from survivors "that 47 people were missing after a raft carrying 125 people from Libya deflated. Eight others were reported separately to have been lost overboard from another boat, and four deaths were reported after fire aboard another."
Di Giacomo said migrant flows to Italy had surged because smugglers in Libya used larger wooden boats, capable of transporting up to 700 people, as well as rubber dinghies good for only 100. "This has had a multiplier effect on departures, and on deaths," he noted.
In Geneva, Spindler said Libyan traffickers were trying to reap as much profit as possible before the Muslim fasting month of Ramadan starts in early June.
The UNHCR said the odds of dying in sea crossings from North Africa to Italy currently stand at 1 in 23, while the migrant death toll for the whole of the Mediterranean this year had risen to 2,510, compared to 1,855 in the same period in 2015.
Nearly 204,000 people have made the dangerous journey across the Mediterranean since January 1, including 46,714 who arrived in Italy, UNHCR said. Nearly all the others travelled from Turkey to Greece before the border was closed in April.
Joel Millman, another IOM spokesman, said in Geneva that although many migrants originally seek jobs rather than refugee protection, many of them end up being trafficked for sex work in Europe and thus "deserve protection."
Meanwhile, police in Italy said that 16 people - 11 from Morocco, two Palestinians, and one each from Ethiopia, Gambia and Egypt - were arrested for operating a migrant smuggling boat that was intercepted Thursday after setting off from Libya.
The men, aged 19 to 36, were charged with abetting illegal migration. Authorities in Catania, Sicily, where the arrests were made, said the suspects extracted payments of 500 euros to 1,000 euros (558 dollars to 1,116 dollars) from each person who wanted to reach Europe.
Before the sea journey, the migrants were held captive for 30-45 days in Zuwarah and Sabrata and fed only once a day. Catania prosecutor Michelangelo Patane said at a press conference that they were given bread and water and beaten with straps.
There were additional arrests of 16 people in Greece and three in the Czech Republic who were suspected of forging documents such as passports and visas and migrant smuggling, according to a Europol statement.
Organized crime groups produced and couriered the falsified documents to EU member states and countries in Africa, the Middle East and Asia, which were then used by migrants to either enter the European Union or towards legalizing their stays once in the bloc.
Europol said there were two crime groups operating in Athens, of Bangladeshi and Sudanese nationals. They charged fees ranging from 100 euros to 3,000 euros per document, such as passports, national ID cards, Schengen visas, driving licences, asylum seeker's registration cards and residence permits.
Czech police uncovered another group that was buying stolen or lost identity and travel documents in the Czech Republic, and sending them to the Athens' gangs to be altered.