Prime Minister Giuseppe Conte, who heads Italy's month-old populist and anti-immigration government, said he would refuse to endorse the conclusions of the meeting in Brussels if fellow leaders fail to do more to help Italy.
"Italy does not need more words, but concrete actions," Conte told reporters as he arrived at the summit. "It's a possibility I hope not to consider, but if we reach that point, on my behalf we will not have shared conclusions."
Sources told the press that the Italian government had made sharing the responsibility of rescuing migrants at sea with its EU neighbours a "red line".
The summit, taking place in Brussels from June 28-29th, is designed to address the tensions between EU members over mass arrivals of migrants, many of whom continue to land in southern Mediterranean countries by boat.
Italy has demanded that current rules requiring asylum seekers to file their application in the first EU state in which they arrive be replaced with a system to distribute migrants across the entire bloc. Such plans are strongly opposed by eastern European countries, particularly Hungary and Poland.
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The Italian prime minister called this week's summit a "watershed" on the issue.
"In the meetings I've had I have received many displays of solidarity," Conte said on Thursday. "Today is a very important day, we're waiting for these statements to be turned into action."
Migration could prove a "make-or-break" issue for the whole of the EU, German Chancellor Angela Merkel said.
"We cannot leave those countries where asylum seekers arrive to deal with [the problem] alone. If we do not get an agreement with the 28 EU member states, we will then need to consider a coalition of the willing on migrant policy," she told the German parliament on Thursday.
"We need to find better solutions."
Meanwhile EU President Donald Tusk issued a fresh warning on the need for action on migration to stave off rising populism and authoritarianism.
"Some may think I am too tough in my proposals on migration, but trust me, if we don't agree on them, then you'll see some really tough proposals from some really tough guys," the former Polish premier added.
The leaders hope at the summit to approve work on migrant "disembarkation platforms" in countries outside Europe, most likely in Africa, according to a draft prepared by Tusk. In a bone to Merkel, the leaders will also agree to "closely cooperate" on stopping secondary movements of migrants, according to draft summit conclusions, although the language may be weaker than she would have hoped.
Italy's new government has taken a strident tone on immigration, with hardline Interior Minister Matteo Salvini declaring the country's ports closed to all NGO ships that pick up migrants at sea.
Ahead of the summit, Spain's Prime Minister Pedro Sanchez called for the "incendiary" talk to be toned down, saying that it might win elections but wouldn't help solve problems.
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Photo: Marco Bertorello/AFP