The German captain of a migrant rescue ship will ask magistrates to block Italian Interior Minister Matteo Salvini's social media accounts because he has used them to spread hate, her lawyer said on Thursday.

The German captain of rescue vessel Sea-Watch 3, Carola Rackete, who was temporarily arrested for bringing migrants to Italy, on Friday strongly criticised both Rome and Berlin.

Interior Minister Matteo Salvini on Wednesday denounced a judge who freed the German captain of a charity rescue ship accused of forcing an Italian naval blockade and suggested the ruling was politically motivated.

An Italian judge ruled on Tuesday that the German captain of a migrant charity ship had not broken the law when she forced a naval blockade at the weekend, saying she had carried out her duty to protect life.

Germany has agreed to take in about a dozen of the 41 migrants who arrived in Italy last month on board German charity rescue ship Sea-Watch, an Italian government source said on Tuesday.

The German captain of a charity rescue ship appeared before a court in Sicily on Monday after she was arrested for forcing her way into an Italian port carrying migrants she had rescued off the Libyan coast.

Sea-Watch 3 skipper Carola Rackete, who risks jail time for forcing her way into Italy's Lampedusa port with 40 rescued migrants, has defended her act of "disobedience", saying she was compelled to avert a human tragedy.

Sea-Watch 3 skipper Carola Rackete faced jail time Saturday after forcing her way into Italy's Lampedusa port with a shipload of rescued migrants to end a lengthy standoff with authorities.