Italian police have arrested four people who had been planning to join Daesh in Syria.

According to local media reports, they may also have been plotting attacks on the Israeli embassy in Rome and the Vatican.

In a news conference, Milan prosecutor Maurizio Romanelli did not specify the targets of the attack, but said that investigators believe one of the suspects asked another to plan an attack in Italy and mentioned Rome.

"The new aspect here is that we are not talking about a generic indication (of an attack) but a specific person being appointed to act on Italian soil," Romanelli said.