An Italian coast guard ship carrying migrants who allegedly made death threats against the crew of a merchant vessel after being rescued in the Mediterranean docked in a port in Sicily on Thursday.

But the 67 migrants on board were not immediately allowed to disembark.

Instead, police and prosecutors boarded the Diciotti patrol ship to try to identify the migrants who made the threats – allegedly two men from Ghana and Sudan.

Rome says they made the threats because they were afraid of being handed over to the Libyan coast guard and sent back to Libya.

Matteo Salvini, Italy’s hardline interior minister, called the alleged aggressors “pirates” and “criminals” and said he wanted them led off the ship in handcuffs.

The migrants were rescued in the Mediterranean by an Italian-flagged oil rig supply vessel, the Vos Thalassa, on Sunday.

They were then transferred to the coast guard patrol ship and brought to the port of Trapani in western Sicily.

Speaking in Innsbruck, where he was attending a meeting of EU interior ministers, Mr Salvini said: “We are in no hurry to let them disembark. If it is shown that some of the migrants were violent, they will go to prison.”

Opposition MPs called him heartless and said that the three women and six children on board should at least be allowed onto dry land.

"Those six children are not criminals and need to be allowed to disembark straightaway," said Debora Serracchiani, an MP from the centre-Left Democratic Party. 

At the EU meeting in Austria, Mr Salvini called for far greater numbers of migrants to be sent back to their home countries.

"Italy has a backlog of 500,000 illegal immigrants and if we don’t manage to expel more than 10,000 a year we’ll take 50 years to make up for the past".

His blocking of NGO rescue boats from Italian ports and his pledge to expel half a million unauthorised migrants living in Italy has gone down well with many voters.

His party, The League, won 17 per cent of votes in Italy’s general election in March but its support has since soared to around 30 per cent.

There are signs that his uncompromising rhetoric may be fomenting racism.

Two Nigerian migrants reported that they were shot at by men with airguns this week while they waited at a bus stop in the town of Latina, south of Rome.

It was the second such incident in a few weeks – last month another pair of African migrants said three Italian youths shot at them with an air gun while yelling “Salvini, Salvini!” in a town near Naples.