The German migrant rescue ship Sea-Watch 3 entered Italy's territorial waters on Wednesday, defying an Italian government ban.
The ship's captain said she decided to head towards the southern Italian island of Lampedusa in the Mediterranean as the conditions at sea were "worse than ever" and claimed that she had the right do do so under the Law of the Sea.
However, Italy's Interior Minister Matteo Salvini issued a strict warning.
"We are warning them: We will use every means allowed by the democratic government to stop this clear infringement of the law. Obviously, the Netherlands government will be accountable for this, as will the Germans, as this NGO and its personnel are German. I'm fed up and I'm talking on behalf of 60 million Italian citizens," he said.
The Sea-Watch 3, which is is owned by a German charity, has been in international waters since June 12 after it rescued 53 people from an inflatable boat about 47 nautical miles north of Libya, and had been waiting near Lampedusa for somewhere to dock.
Italian authorities allowed 10 people to disembark for medical reasons, but they denied the vessel entry into Italian waters based on the so-called Salvini order, which bans the docking of vessels that constitute a danger to security and public order.