Matteo Salvini, who leads the anti-migrant League party, tweeted the warning on Monday after the Eleonore entered Italian waters without permission and sailed towards a Sicilian port, where it was seized by Italian authorities.
Mission-Lifeline captain Claus-Peter Reisch said bad weather forced him to bring the refugees to Pozzallo’s port after they were stranded on board for eight days by the outgoing populist Italian government’s crackdown on humanitarian rescue boats.
The German foreign ministry said they are in contact with Italian officials over the situation, adding “a good and quick solution” needs to be found.
Spurred by far-right Mr Salvini, the Italian government has issued a decree establishing €1m (£909,000) fines for captains of rescue boats that defy the ban on entering Italian waters or docking without permission.
Since authorities have seized the Eleonore, it appears they will let the refugees disembark.
It comes as Greek authorities have begun transporting about 1,500 asylum-seekers from the eastern Aegean island of Lesbos to the mainland, as part of government efforts to tackle overcrowding in refugee camps and a recent spike in the number of people arriving from the nearby Turkish coast.
A ship carrying 635 people set sail from Lesbos on Monday morning for the northern port city of Thessaloniki.
From there, authorities said the asylum seekers would be transported to a camp in Nea Kavala in northern Greece.
A second ship carrying around 900 people was to leave Lesbos for Thessaloniki on Monday afternoon.
The transfer was part of decisions made during a national security meeting convened by the Greek prime minister, Kyriakos Mitsotakis, on Saturday, after nearly 600 people arrived on Lesbos in the space of an hour on Thursday.
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