The number of migrants dying in Mediterranean Sea crossings could hit 30,000 this year if the current rate continues, the International Organisation for Migration (IOM) says.
The deaths in 2015 so far are 30 times higher than the same period last year.
The UN believes the sinking of one boat at the weekend claimed over 800 lives, making it the deadliest recorded.
The Tunisian captain of the boat survived and has been accused in Italy of reckless multiple homicide.
Prosecutors there allege Mohammed Ali Malek, 27, steered his heavily overloaded boat into collision with a merchant vessel coming to its rescue.
Locked below decks
IOM spokesman Joel Millman told reporters in Geneva: "The 2015 death toll now is more than 30 times last year's total at this date... when just 56 deaths of migrants had been reported on the Mediterranean.
"IOM now fears the 2014 total of 3,279 migrant [deaths] on the Mediterranean may be surpassed this year in a matter of weeks, and could well top 30,000 by the end of the year, based on the current death toll. It could actually be even higher."
More than 1,700 migrants are believed to have died so far in 2015.
They've become the most important witnesses in an official criminal investigation into the wreck of their boat. Italian officials instructed us not to approach or speak to them.
After midday the survivors came out of the house and were escorted the few steps to a waiting minibus. The survivors - all young men - boarded the bus in single file and in silence.
One of them sat next to the window. I caught his eye and signalled a thumbs up or thumbs down sign as a question. He replied with a thumbs up - and then broke out into a smile.
The survivors were then driven a short distance to the dining hall, where they were served a lunch of pasta, rice, chicken and vegetables. They ate in silence.
Meanwhile a spokesman for the UN refugee agency said it had interviewed most of the 28 survivors of the weekend sinking off Libya.
Adrian Edwards said it appeared more than 800 people had died - "the deadliest incident in the Mediterranean that we have recorded".
About 350 on board were believed to be Eritreans, with refugees from other nations including Syria, Somalia, Sierra Leone, Mali, Senegal, Gambia, Ivory Coast, Ethiopia and Bangladesh.
Prosecutors in the Sicilian port of Catania, where the survivors were brought, say Capt Malek is also accused of people-smuggling.
His first mate, 25-year-old Syrian Mahmud Bikhit, also survived and faces unspecified charges.
The charges on both men have yet to be formally laid by a judge.
Prosecutors say the boat collided with a Portuguese container ship just before it capsized, but cleared the merchant vessel's crew of any responsibility.
Source: BBC News
