Italy set high demands on Thursday for any European Union deal on migration, which German Chancellor Angela Merkel urgently needs to stave off a coalition crisis at home.
Arriving for what is certain to be fraught talks over dinner in Brussels, leaders of Spain, Greece, Finland and Luxembourg backed Merkel's push to curtail "secondary migration" of people who arrive at the EU's southern border and then head north to Germany across the bloc's control-free travel zone.
But Italian Prime Minister Giuseppe Conte said he could block any agreement unless other EU states also agree to allow in their ports boats carrying people across the Mediterranean.
They will spar behind closed doors but attempt a show of unity in public, agreeing tougher new measures to stem arrivals from the Middle East and Africa to Europe in the first place.
"I suggest we focus on the EU's external border, including the disembarkation platforms project," the chairman of the 28 EU leaders' talks, Donald Tusk, said of a new idea to set up sites around the Mediterranean where the EU would decide on asylum.
"The alternative to this solution would be a chaotically advancing closure of borders, also within the EU, as well as growing conflicts among EU member states," he said, reminding bloc leaders that echoes of their failed response to a 2015 spike in sea arrivals was still feeding support for eurosceptic, populist and anti-migration groups across the bloc.
Merkel, the EU's longest-serving leader, has come under acute political pressure from her hardline allies in Bavaria who are threatening to close their border to migrants if she can't work out a deal with European partners.
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That could trigger the collapse of Merkel's three-month-old government and cause the EU's Schengen free travel zone to unravel, putting cross-border business, trade and many jobs among the EU's 500 million people at risk.
Spanish Prime Minister Pedro Sanchez told reporters that European solidarity on migration was vital, "especially with Germany which is now suffering a political crisis".
Luxembourg's Prime Minister Xavier Bettel added: "There are so many people who arrived in different countries and then made their way to Germany. I understand when Germany says 'Why do we have to deal with everything’?"
Greece's Alexis Tsipras and Finland's Juha Sipila and diplomats from several other EU states also promised to work with Germany on the issue.
Merkel has called on European leaders to forge a common approach to migration, calling it a "make or break" issue.
"Europe faces many challenges, but that of migration could become the make-or-break one for the EU," said Merkel, whose 2015 decision to open Germany's borders to hundreds of thousands of refugees divided Europe and continues to haunt her at home. "Now as then, I think that was the right thing to do," she told a speech in the Bundestag earlier on Thursday.
According to draft conclusions circulated before the two-day summit, the leaders will agree measures to strengthen Europe's external borders, spend more on fighting illegal immigration and step up cooperation to prevent refugees and migrants from moving within the bloc.
They will give more money for Syrian refugees in Turkey and migration projects in Africa, as well as look at sealing a deal with Morocoo to reverse a recent uptick in arrivals in Spain.
But the EU remains deeply divided over how to handle asylum seekers, with the ex-communist easterners led by Poland and Hungary refusing to accept a share of the new arrivals to alleviate the burden on Italy and Greece, struggling to cope.
A deal among all 28 EU states is unrealistic, so Merkel is pushing for a "coalition of the willing" on migration. She hopes that will appease the Christian Social Union (CSU), which has hardened its line before an autumn election in its home region of Bavaria, the main German entry point for migrants.
Convincing Italy to do a deal may be the biggest challenge. Its new eurosceptic government, which includes the anti-establishment 5-Star movement and far-right League, has rejected any moves that would make it handle more migrants.
At stake is EU members' unity and trust in each other, as well as the Schengen zone but the bloc is turning increasingly restrictive on immigration, with surveys showing it is the top concern for EU citizens.