Italian port authorities have impounded the German-flagged NGO ship Sea-Watch 4 in Palermo after an 11-hour inspection, aid organisations who operate the vessel said on Sunday.

According to the groups, which include Germany's Protestant Church (EKD) and Doctors Without Borders (MSF), officials had justified the measure by saying saving people was not in accordance with the ship's registration.

Among other things, the Italian authorities objected that the vessel had too many life jackets on board and that the sewage system was not adequate for the number of people rescued.

Italy impounded a German humanitarian ship that was on a mission to rescue migrants in the Mediterranean https://t.co/ECF2vPNKiO

— The National (@TheNationalUAE) September 21, 2020

"These flimsy excuses show once more that it is not a matter of checking the ship's safety, but a deliberate measure to prevent civilians carrying out sea rescues in the central Mediterranean," said Philipp Hahn, head of operations on the Sea-Watch 4.

Another of the groups operating the ship, United4Rescue, said that German authorities had confirmed to the Sea-Watch NGO in July that the ship met all safety requirements.

The Sea-Watch 4 has been in the Sicilian port of Palermo since early September when it brought rescued refugees and migrants to a quarantine vessel there.

The crew has gone through two weeks of quarantine because of the coronavirus pandemic.