Migrants have kidnapped a merchant ship that rescued them from the coast of Libya and ordered the crew to sail to Malta, reports said.
Malta's military said the ship would not enter its waters. Italy's Deputy Prime Minister Matteo Salvini described the kidnappers as "pirates".
The EU says it will end naval patrols in the Mediterranean.
The EU's decision to close Operation Sophia in September follows the request of Italy.
The mission was set up four years ago to hold people smugglers and rescue migrants trying to reach Europe by boat. Tens of thousands were saved.
More recently, the mission has targeted smuggling networks, with the number of people crossing the river dropping sharply following a controversial agreement between the EU and Libya.
But Mr. Salvini, leader of the right-wing league party, has accused Operation Sophia of continuing to bring rescued migrants to the Italian coasts.
What about the abducted ship?
The cargo ship Elhiblu is said to have carried more than 100 migrants. The current location is unclear, as are the circumstances of the rescue from Libya.
The Libyan Coast Guard has not commented publicly on the reported kidnapping.
A spokesman for the Maltese armed forces said attempts to contact the ship's captain were unsuccessful, reports the website of the MaltaToday website.
Maltese officials monitored the situation and were prepared for any eventuality, the spokesman added.
Meanwhile, Mr Salvini wrote on his Facebook page (in Italian): "They are not shipwrecked but pirates, they will see Italy only through a telescope."
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Mr. Salvini was at the center of a series of international conflicts over a refusal to allow migrants to dock in Italian ports.