Italy on Sunday prepared to let vulnerable migrants off a second rescue ship for charities in Sicily, but sources close to Minister Matteo Salvini warned those not eligible to stay would be pushed back into international waters.

Minors and the sick were left in the port of Catania by the German-flagged Humanity 1 in the early hours of the morning, but 35 adult male migrants were refused permission to set foot on Italian soil, charity SOS Humanity said.

The humanitarian aid ship Geo Barents, operated by MSF and flying the Norwegian flag, said it had also been summoned so authorities could assess “vulnerable cases” among the 572 people rescued on board.

Interior Minister Matteo Piantedosi previously said those who don’t “qualify” would have to “leave territorial waters” after refusing requests for a safe harbor from four charity ships.

The Geo Barents, Ocean Viking and Rise Above still carry 900 migrants.

Italy’s new far-right government, sworn in last month, has vowed to crack down on boat migrants attempting the dangerous crossing from North Africa to Europe.

According to the Interior Ministry, over 87,000 people have landed in Italy so far this year – although only 14 per cent of them have been rescued at sea and taken to safety by charity ships.

Sources close to far-right Transport Minister Matteo Salvini, who controls the ports, said the Geo Barents was only temporarily allowed on Sunday.

“Those staying on the ship will be provided with the necessary assistance to exit territorial waters,” the sources said.

The 35 migrants who were denied permission to leave Humanity 1 are “extremely depressed,” SOS Humanity spokeswoman Petra Krischok told AFP.

It was unclear whether the ship would be asked to leave the port.

“For now, we’re going to stay here and wait,” she said.

The leader of the largest opposition party, the head of the Democratic Party, Enrico Letta, accused the government of breaking international law on Twitter.

Piantedosi should explain his actions to Parliament, the party said.

MP Aboubakar Soumahoro, who was present when the chosen ones disembarked from Humanity 1, criticized the “selection of shipwrecked migrants”.

He said the government of far-right Prime Minister Giorgia Meloni “treats as objects the worn-out bodies of shipwrecked people, already exhausted from cold, fatigue, trauma and torture…”.

“If the remaining castaways are rejected… we will challenge this decision in all appropriate institutions,” he said on Twitter.

Piantedosi said on Saturday that the migrants who are not allowed to disembark would have to be “cared for by the flag state” – a reference to the national flags under which the ships sail.

Humanity 1’s Rise Above and Mission Lifeline sail under the German flag.

SOS Mediterranee’s Geo Barents and Ocean Viking are registered in Norway.

Norway’s foreign ministry said Thursday it had “no responsibility” for those rescued by private Norwegian-flagged vessels in the Mediterranean.

Germany, in a diplomatic “note” to Italy, insisted the charities “make an important contribution to saving lives” and asked Rome to “help them as soon as possible”.