The UN congress on crime and justice aims to fix migration and forced labour issues, but no date set for solutions.
A dozen African migrants have died after being thrown overboard by fellow passengers, Italian police say, and another 41 boat migrants are feared to have drowned in a separate incident.
Police in the Sicilian port of Palermo said on Thursday they had arrested 15 migrants suspected of attacking other passengers after a religious row on a boat headed for Italy, which is struggling to cope with a huge surge in illegal migrants arriving on its shores.
The 15 men were accused of “multiple aggravated murder motivated by religious hatred,” police said in a statement.
The police said those arrested were Muslims while those thrown overboard were Christians.
The 12 victims were all Nigerians and Ghanaians while the 15 suspects came from Senegal, Mali and Ivory Coast.
Distraught survivors, who set off from Libya on Tuesday before being rescued by an Italian vessel on Wednesday, told a “dreadful” story of “forcefully resisting attempts to drown them, forming a veritable human chain in some cases”, police said.
In another incident, 41 migrants were missing, feared drowned after their dinghy sank en route to Italy, the International Organisation for Migration (IOM) said, just days after 400 migrants were believed to have died in another shipwreck off the coast of Libya.
The four survivors of Thursday’s shipwreck, who came from Nigeria, Ghana and Niger, said their boat sank after setting sail from Libya with 45 people on board.
Their vessel was spotted by a plane which alerted the Italian coastguard, but by the time a navy ship arrived to help them, only four passengers were found alive.
The latest deaths bring the number of migrants killed while attempting to cross the Mediterranean Sea this year up to 900, the IOM said, up from 96 between January and April last year.
IOM said about 10,000 people had been rescued off Italy since Friday alone, with recent good weather prompting a rise in the number of migrants attempting the risky crossing, many of them fleeing conflict and poverty in Africa and the Middle East.
The flood of people trying to reach Italy in recent days has been “extraordinary”, IOM’s Giovanni Abbate said in the Sicilian port of Augusta, where more new arrivals were disembarking.
Al Jazeera’s Paul Brennan, reporting from Augusta, said volunteers were called in to assist doctors because of the enormous influx of people.
“What they have seen hauled from the water in recent weeks is harrowing,” he said.
He quoted a doctor as saying: “We see people who have swallowed water and gasoline. It’s awful.”
Italy pleaded for more help on Thursday from other European Union countries to rescue the migrants and share the burden of accommodating them.