Rome police chief Nicolò D'Angelo said there would be the highest level of security around the Colosseum, with police positioned at public entrance points, as well as the nearby Via del Corso, Rome's main shopping thoroughfare.
There will also be maximum security in the area surrounding St Peter's, including the Vatican Museums, as well as at various churches and places of worship within the centre and in Rome's outskirts.
Security will also be tightened at outdoor events such as concerts and at shopping centres and ports.
The announcement came as another video, purporting to be from Isis jihadists and threatening again “to conquer Rome”, alongside images of Piazza Navona, was released, Il Messaggero reported. There have been several similar videos over the past couple of years.
Interior Minister Angelino Alfano said in July that the country had intensified security due to a “resurgence of jihadist threats”. The announcement came a day before 84 people, including five Italians, were killed in an attack in the southern French coastal city of Nice.
Italy's security alert level has been at 2, the highest possible in the absence of a direct attack, since the Paris attacks in November last year.