Police in Naples have arrested a firework retailer suspected of being a sympathiser of the Islamic State (Isis/Daesh) terror group. The 30-year-old man, identified as Diego Oddati Menna, was arrested in his home in San Gennaro Vesuviano after police monitored his activities on social media for days.

The man had praised IS activities on Facebook, where he posted under the names Michele Menna or Diabolik U Siccu. Among other things, Menna shared a video of IS beheading a captive and called for similar executions of some of his countrymen, Italian media reported.

During a raid at the man's house, police and bomb disposal specialists found home-made mortar shells, 146 fuses, various detonators and electronic devices used to set off explosives remotely. Authorities defined him as an "explosive expert".

Menna is also a sympathiser of the Naples-based mafia known as Camorra and the Sicily-based Cosa Nostra and praised on social media mafia bosses, particularly Sicilian boss Matteo Messina Denaro, known as Diabolik.

At his house, police found posters, photographs and newspapers articles of mob bosses.

Following the arrest, interior minister Angelino Alfano praised the security forces for their fight against terrorism.