More than 100 migrants aboard the cargo ship Elhiblu I are said to have acted after being told they would be taken back to Libya.
Interior Minister and leader of the right-wing League party Matteo Salvini said that the ship had been heading north when “it made an abrupt change of course after the vessel had arrived six miles from the entry into the port of Tripoli [the capital of Libya]”.
Salvini said there was no chance of the migrants being allowed to land in Italy, describing the event as “the first act of piracy on the high seas”.
“They should know that they will only see Italy with a telescope,” he added.
The hijacking comes as the EU cuts back on navy rescue patrol missions in the Mediterranean.
The EU is planning to suspend Operation Sophia in September, in response to pressured requests by Italy, where anti-migrant sentiment is rising.
The operation was put in place four years ago to deter people smugglers and rescue migrants trying to reach Europe by boat.
Tens of thousands of refugees have been intercepted.
More recently, 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, which saw millions of euros put into funding the Libyan coastguard, which intercepts boats heading for Italy and returns refugees and migrants to Libya, a war zone.
There are roughly 7,000 people in “official” Tripoli detention centres, including 640 children, according to the UN.
Meanwhile, the city of Tripoli is experiencing its worst bouts of fighting in years, as the Libyan civil war persists.
Salvini, however, blames Operation Sophia for continuing to bring rescued migrants to Italian shores.
He has been at the centre of a number of international rows over his refusal to allow migrant ships to dock in Italian ports.
