Italian anti-terrorism police said on Wednesday they had arrested an Italian citizen of Moroccan origin on suspicion of supporting Islamic State and were investigating his accomplices.

It was the latest in a series of arrests this month involving suspected supporters of terrorism and came as Italy steps up the number of foreigners it expels.

A statement identified the arrested man as Elmahdi Halili, 23, who was arrested in the northern city of Turin.

Police said Halili had received a two-year suspended prison term in 2015 for ‘instigating terrorism’ by running a website that praised Islamic State and hailed some of the attacks it or its supporters carried out in Europe.

The police operation targeted an undisclosed number of other people, both foreign and Italian, some of whom had converted to Islam and were part of ‘a campaign of radicalisation’. It was not clear from the statement if they also had been arrested.

Details of the operation, in which about 13 homes were searched, were due to be announced at a news conference later on Wednesday.

In an interview published on Wednesday in the Turin newspaper La Stampa, Interior Minister Marco Minniti said the security threat to Italy from supporters of Islamic State was higher than ever.

Minniti said this was because more so-called foreign fighters would be attempting to return to Europe via Italy after IS suffered a series of defeats in Syria and Iraq.

Wednesday's operation was the latest in a string of arrests in Italy of people suspected of supporting Islamic State.

On Tuesday in the southern city of Foggia, police arrested an Egyptian-born man suspected of being a member of Islamic State and of indoctrinating young children in a cultural centre he ran.

On March 15, police acting on a tip from the US FBI arrested a man of Latvian origin who they said had been preparing pipe bombs. A judge's detention order said the man had been considering an attack on a kindergarten.

In recent months, Italy has stepped up expulsions of foreigners believed to be a threat to national security. So far this year, 29 people have been expelled.