Migrants have hijacked a merchant vessel that rescued them off Libya's coast, ordering the crew to head towards Malta, reports say.
More than 100 migrants aboard the cargo ship are said to have acted after being told they would be taken back to Libya.
Malta's military said the ship would not be allowed into its waters. Italy's Deputy Prime Minister Matteo Salvini described the hijackers as "pirates".
This comes as the EU says it is ending navy patrols in the Mediterranean.
The EU says the decision to suspend Operation Sophia in September follows a request by Italy.
The mission was put in place four years ago to deter people smugglers and rescue migrants trying to reach Europe by boat. Tens of thousands have been saved.
Lately, the mission has largely targeted smuggling networks as the number of people making the crossing dropped sharply following a controversial deal between the EU and Libya.
But Mr Salvini, the leader of the right-wing League party, has blamed Operation Sophia for continuing to bring rescued migrants to Italian shores.