A German charity has said its rescue ship was impounded by Italian authorities for breaching tougher migration rules introduced by the country's right-wing government as part of a crackdown on NGO sea-rescue activities.

The Mare*Go organisation said on Friday that it disobeyed instructions to take 36 migrants it picked up on Thursday to the Sicilian port of Trapani, taking them instead to Lampedusa island, saving itself hours of navigation.

"The rescue ship is blocked for 20 days" in Lampedusa, the NGO in a statement, adding it would also "likely face a fine because we broke the new Italian Decree Law" sponsored by Prime Minister Giorgia Meloni.

Noting that Trapani was 32 hours away from the location where the migrants were picked up, the NGO tweeted: "We clearly communicated to the authorities that #MareGo is not equipped to treat the rescued people on the move for that period of time".

The Italian law, approved by parliament in February, requires charity-run ships to head to port immediately after a rescue, preventing them from carrying out multiple operations at sea.

Italian authorities have also started a practice of instructing ships to head to more distant ports, not just in Sicily but further up the Italian peninsula, in some cases hundreds of kilometres away.

Charities that do not comply with the rules risk fines and the impounding of their vessel.

Investigation over shipwreck

In other news, three members of Italy’s border police force are under investigation for a suspected role in a shipwreck off the country’s southern coast this year that killed more than 90 migrants, Italian news outlets reported on Friday.

Quoting from a search warrant issued by prosecutors, the Corriere della Sera newspaper said investigators cited “significant anomalies” in the activity log for a motorboat Italian border police used in an abandoned search for the overcrowded migrant vessel.

A surveillance aircraft operated by the European Union's border and coast guard agency Frontex first spotted the old wooden boat in the Ionian Sea on the night of February 25.

The agency indicated to Italian authorities that no life vests were visible but the boat showed no signs of distress.

Italy’s Guardia di Finanza, or financial police, which also has a border and customs role, dispatched two patrols to “intercept the vessel.” Not long after the search was called off due to bad weather, the migrant vessel broke apart after ramming a sandbank in Calabria, the “toe” of the Italian peninsula.

Some 80 people survived. The known death toll was put at 94 after bodies were recovered in the sea or washed up on beaches, some of them weeks later. An undetermined number of migrants were believed to be missing.

According to Italian news reports, the three border police personnel are being investigated on suspicion of manslaughter, wrongdoing related to official documentation and causing a shipwreck. It wasn’t immediately clear if they participated in the search or were in port giving orders.

Besides the border police members, three other people are being investigated, news channel Sky TG24 and other Italian media reported. Corriere della Sera said the search warrant order blanked out the names of the other three.