Fourteen migrants have drowned in the latest boat sinking as European Union and African leaders gathered in Malta to discuss measures to stem the flow of people into Europe.
Seven of those who died when a wooden boat sank between Turkey and the Greek island of Lesbos were children.
Coastguards rescued 27 survivors.
The meeting in the Maltese capital Valletta was planned after about 800 died in a migrant boat sinking off Libya in April.
The UN says nearly 800,000 migrants have arrived in Europe by sea so far in 2015, while some 3,440 have died or gone missing making the journey.
Some 150,000 people from African countries such as Eritrea, Nigeria and Somalia have made the dangerous journey across the Mediterranean from Africa so far this year, arriving mainly in Italy and Malta.
But this has been dwarfed by the arrival of some 650,000 people – mostly Syrians – via Turkey and Greece.
At the two-day Malta summit, EU leaders are expected to offer countries in Africa billions of euros in exchange for help with the migrant crisis.
The European Commission is setting up a €1.8bn “trust fund” for Africa and has urged member states to match that sum. However, there are doubts about whether they will do so.
The aim is to tackle the economic and security problems that cause people to flee, and persuade African countries to take back more failed asylum seekers.
African leaders are likely to insist on a much clearer path for smaller numbers of their citizens to migrate officially to Europe, in exchange for help on the crisis, says the BBC’s Chris Morris in Malta.
Tensions in the EU have been rising because of the pressures faced by those countries where most migrants initially arrive, particularly Greece, Italy and Hungary. Most migrants then head to Germany or Sweden – regarded as the most welcoming to refugees – to claim asylum.
EU leaders have agreed a controversial programme to relocate thousands of migrants – but so far only about 130 have been successfully moved from Greece and Italy.
Developments on Wednesday highlighted deep divisions between EU members on the migrant issue.
Hungary was bitterly critical of Germany’s announcement that it planned to send more Syrian refugees back to the first EU country they had entered, after reinstating the EU’s Dublin Regulation on asylum. Berlin said this would not include Greece, the first point of entry for most migrants.
Hungarian Foreign Minister Peter Szijjarto said: “The Dublin system is dead.”
He also accused German politicians of making “irresponsible statements” which some migrants had interpreted as an invitation to come to Europe.
Meanwhile, Slovenia has begun building a razor-wire fence along its border with Croatia, a day after the government said it would install “temporary technical obstacles”, but stressed official border crossings would remain open and that the move was designed to restore order.
Croatia criticised the Slovenian fence, saying it would be better to spend money on preparing reception centres for migrants.