ROME - A German charity vessel was on Tuesday impounded by Italian authorities after it ran into a dispute with the Libyan coast guard over the rescue of as many as 100 migrants in international waters.

Italy often temporarily blocks the operations of charity-operated rescue vessels on the basis of a migration decree introduced last year by Prime Minister Giorgia Meloni's rightist government.

The Humanity 1, operated by the SOS Humanity organisation, was blocked for 20 days in the southern port of Crotone, where it had docked on Monday bringing ashore 77 migrants it had picked up during the weekend.

A spokesperson for SOS Humanity said the charity was "falsely accused" of failing to coordinate with Libyan authorities and of putting migrants' lives at risk during a sea rescue.

SOS Humanity said it intervened on Saturday to help 90-100 migrants on three boats in distress in international waters off Libya and Tunisia, and that a Libyan patrol boat tried to stop its efforts by force.

The charity said Libyan officers threatened its staff and migrants with a machine gun. The organisation said the intervention resulted "in people jumping in the water and at least one person drowning" and the separation of family members, as some migrants were picked up by the NGO and some by the Libyans.

Libyan authorities did not respond to a request for comment.

Under international humanitarian law, migrants cannot be forcibly returned to countries where they risk serious ill-treatment, and widespread migrant abuse has been extensively documented in Libya.

At the same time, Italy and other European Union governments are trying to curb the inflow of sea migrants from North Africa, and have offered money or equipment to Libya and Tunisia to stop departures from their shores. REUTERS