ROME — Italy has ordered the seizure of the Aquarius, the rescue ship at the center of international criticism over its government’s hard line against migration, saying the vessel had illegally disposed of potentially infectious waste.

Prosecutors in the Sicilian city of Catania announced on Tuesday that they had accused 24 people of having “systematically shared, planned and executed an illegal waste-disposal project of an enormous quantity” in southern Italian ports between January 2017 and May 2018. They said the waste included contaminated garments, leftover food, and medical supplies and syringes.

Those accused included members of Doctors Without Borders, one of the aid groups operating the Aquarius, and officials of a Sicilian company that manages waste disposal. According to a statement by the prosecutors’ office, the Aquarius and VOS Prudence, another rescue ship operated by Doctors Without Borders, illegally coordinated with the Sicilian company, which failed to declare the “presence of dangerous sanitary waste with an infectious risk.”

Doctors Without Borders denied the accusation in a statement on Tuesday, writing that it “strongly condemns” the Italian order to seize the Aquarius. It called the measure a disproportionate reaction designed to criminalize humanitarian and medical missions at sea. The group said it would appeal in Italian court.