BRUSSELS — With another migrant rescue ship stranded in the Mediterranean and both Italy and Malta again refusing to let it dock, European Union leaders will try to find common ground for tackling a growing political crisis that is threatening to undermine the entire EU.

The leaders of about 16 countries – more than half the 28-nation bloc – will take part in what is being billed as “informal talks” in Brussels on Sunday ahead of a full EU summit next Thursday and Friday, where migration will top the agenda.

“These rescue ships can forget about reaching Italy,” Italy’s new firebrand interior minister, Matteo Salvini, said Saturday as he assured his anti-migrant base that he would “crush” the human trafficking business.

At the heart of the problem lie deep divisions over who should take responsibility for arriving migrants – often Mediterranean countries like Italy, Greece and increasingly Spain – how long they should be required to accommodate them, and what should be done to help those EU countries hardest hit.

The problem was crystalized recently in a row between Italy’s new populist government, Malta and France over who should take responsibility for 630 people rescued from the Mediterranean Sea off the coast of Libya, the main departure point for people trying to reach Europe.

Amid the mud-slinging, Spain’s new Socialist government agreed to take charge of the migrants and the ship eventually made a weeklong voyage to Valencia.

Spain announced Saturday it rescued 569 more migrants at sea, many from the Strait of Gibraltar, a busy shipping lane with treacherous currents.