Humanity 1 refuses to leave until Italy allows everyone to disembark.
Italy's new right-wing government is in a standoff with a German-registered migrant rescue ship, Humanity 1, after refusing to allow 35 passengers to disembark in Sicily on Sunday.
Following a medical inspection on board, Italian authorities let 144 people off the ship, including children, pregnant women and those deemed "vulnerable".
However 35 others - all adult males - were barred from disembarking into the port of Catania and the ship was ordered to leave Italian waters.
Italian interior minister Matteo Piantedosi said those who did not qualify as vulnerable should be taken care of by the "flag state".
However the captain of the ship, Joachim Ebeling, is refusing to leave Catania port "until all survivors rescued from distress at sea" are given safe harbour.
The Berlin-based charity SOS Humanity on Monday announced that it would take legal action against the Italian government whose "selective and partial disembarkation" policies are "illegal and unacceptable" and "violate European law & the Geneva Refugee Convention".
On Sunday a second charity ship arrived in Catania - the Geo Barents operated by Medecins sans Frontieres (MSF) - with Italian authorities allowing 357 to disembark but blocking 215 on board.
Two other boats run by non-governmental organisations are still waiting for permission to enter Italian waters: the German Rise Above, carrying 90 people, and the Norwegian Ocean Viking, with 234 people.
Italy's deputy premier and former interior minister Matteo Salvini hit out at the perilous sea crossings by migrants, describing them as "organised trips". "Those aboard those ships pay around $3,000, which become weapons and drugs for the traffickers", he told Radio RTL 102.5.
Italian-Ivorian trade unionist and newly-lected parliamentarian Aboubakar Soumahoro, who boarded Humanity 1 at the weekend, urged Meloni's government to allow those still on board to disembark, describing their rejection as "illegal and inhumane".
Soumahoro accused the government of using the migrants to distract from other issues including energy bills, saying: "The fault of the migrants is to speak another language, to have another colour."
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