Italian PM Matteo Renzi has led calls for more European Union action on sea migration after the latest deadly capsize of a boat in the Mediterranean.
Demanding a summit on the issue, Mr Renzi said trafficking was “a plague in our continent” and bemoaned the lack of European solidarity.
The 20m (70ft) long boat was believed to be carrying up to 700 migrants, and only 28 survivors have been rescued.
EU foreign ministers are expected to address the issue at a meeting later.
Human smugglers are taking advantage of the political crisis in Libya to use it as a launching point for boats carrying migrants who are fleeing violence or economic hardship in Africa and the Middle East.
Up to 1,500 migrants are now feared to have drowned this year alone.
The UN High Commissioner for Refugees (UNHCR) said the latest sinking could amount to the largest loss of life during a migrant crossing to Europe.
’21st Century slavery’
Mr Renzi singled out Libya as the key problem, saying it was the starting point for about 90% of the migrants reaching Italy by sea.
He said more rescue boats was not the issue, rather it was stopping the boats from departing.
Analysis: BBC world affairs correspondent Richard Galpin
Presidents, prime ministers and the Pope have all described their horror at the massive loss of life and spoken of the need to do something quickly to stop it.
But will their powerful and emotional statements lead to a new EU approach to tackling the migrant crisis, including the provision of more ships capable of search and rescue?
Deep divisions between the 28 EU member states were laid bare last year when Italy stopped its search-and-rescue operations after plucking more than 100,000 people from the sea.Some Italian politicians had called for a naval blockade but Mr Renzi said this would only help the smugglers as there would be more ships to rescue migrants.
Some Italian politicians had called for a naval blockade but Mr Renzi said this would only help the smugglers as there would be more ships to rescue migrants.
Calling trafficking “the slavery of the 21st Century”, he added: “It is unthinkable that in the face of such a tragedy, there isn’t the feeling of solidarity which Europe has shown in other instances.”
Mediterranean migrants
13,500: Migrants rescued 10-17 April
900: Migrants died attempting the crossing between 1 Jan and 15 April
31,500 Migrants have arrived from North Africa so far this year
218,000 Estimated to have crossed the Mediterranean in 2014
3,500 Migrants died attempting the crossing last year
Fellow European leaders echoed Mr Renzi.
French President Francois Hollande called for “more boats, more over flights and a more intense battle against people trafficking”, while Maltese PM Joseph Muscat said Europe and the international community would be judged by history if they continued to “turn a blind eye” to the plight of migrants.
Spanish PM Mariano Rajoy said: “This is the umpteenth time we hear of yet another human tragedy in the Mediterranean… Words won’t do any more.”
The EU has been criticised for its policy since the rescue operation, Mare Nostrum, was ended last year. Some EU members said they could not afford it and expressed concerns that it was encouraging more migrants.
It now runs a more limited border control operation called Triton.
A spokesperson for UN Secretary General Ban Ki-Moon said the deaths were an “urgent reminder of the critical need for a robust search and rescue capacity in the Mediterranean”.
The international community had a duty to ensure the right to asylum for those fleeing war in search of safety, he added.
The latest boat to sink went down on Saturday night, 130 miles (210km) off the Italian island of Lampedusa and 17 miles from the Libyan coast. So far only 24 bodies have been retrieved.
The migrants reportedly fell overboard when they rushed to draw the attention of the passing Portuguese merchant ship King Jacob, causing their ship to capsize.
One survivor in the Cannizzaro hospital in Catania, Sicily, said there were as many as 950 people on board, although this has not been verified. He said many were locked below decks and not allowed to leave.
The UNHCR said that migrant boats had carried 13,500 people into Italian waters last week alone.
Last year, a record 170,000 people made the perilous crossing to Italy. Thousands died on the journey.
Recent Mediterranean migrant disasters
Oct 2013: More than 360 people, mostly Eritreans and Somalis, die as their boat sinks off Lampedusa.
Sept 2014: At least 300 migrants drown off Malta when people smugglers ram a boat after its occupants refuse to move to a smaller one. Survivors said it was “mass murder”.
Feb 2015: At least 300 migrants feared drowned as four dinghies get into trouble after leaving Libyan coast in bad weather.
April 12, 2015: Some 400 migrants feared drowned after their vessel capsizes off Libya.
April 19, 2015: About 650 migrants feared drowned as boat capsizes in Libyan waters south of Lampedusa.
