Open Arms said its eponymous ship had been subjected to a new 20-day blockade and a fine of up to €10,000.

The ship was also detained in August along with two other rescue vessels accused of breaking a contested new law that states charities must return to port between every rescue, and only to the port designated by Italian authorities.

Open Arms yesterday disembarked 176 migrants in the Tuscan port of Carrara who had been rescued in three operations in the Central Mediterranean.

In a statement today, it accused Italian prime minister Giorgia Meloni’s government of a “strategy of harassing the work of humanitarian ships”.

“We will bear this unjust detention and the resulting legal costs,” it said.

“But we find it unacceptable to have to suffer this situation because we have done our duty, respecting the Law of the Sea and international conventions.”

Meloni’s government took office one year ago pledging to end irregular migration, but the numbers have surged.

More than 135,000 migrants have landed on small boats on Italian shores so far this year, up from 72,400 in the same period of last year, interior ministry figures show.

Only about 5% of migrants are picked up by charity ships, the government says.

However, Meloni claims the rescuers encourage smugglers, a finding challenged by researchers who have highlighted the complex reasons that drive migration – not least the weather, with crossings increasing when seas are calm.