Italy has not suffered any jihadist attacks on its territory but has been repeatedly warned by Isis propagandists that the country and the Vatican are on its hit list, most recently in messages relayed over the Telegram messaging service this weekend.
According to the Italian media, an extra 50 police carrying portable scanners were on duty to carry out checks on the 10,000 people who were in St Peter's square Sunday for Pope Francis's weekly Angelus prayer.
But the Vatican played down the reports. "We are not aware of any increased measures. As far as we are concerned the level of vigilance was already very high," a spokeswoman said.
Francis told pilgrims he shared the pain of attack victims. "We pray for the dead, the injured and all those close to them, and we beg the Lord, God of mercy and peace, to free the world from this inhumane violence."
The prefecture which oversees security in Rome decided Saturday to increase preventive measures at major pedestrian sites seen as potentially vulnerable to the kind of deadly vehicle attacks seen in busy locations in Barcelona, Nice, Stockholm, Berlin and London.
The measures were not specified. Media reports said new concrete barriers were planned for part of the famous shopping street Via del Corso, and for the Roman Forum area.
Concrete blocks have been in place for some time on the Via della Conciliazione, the main road leading to St Peter's square.
New barriers capable of preventing vehicles entering areas with large numbers of people on foot have appeared in recent days in central Milan, Bologna and Turin and barriers around pedestrian areas are planned in Palermo.
In Bologna, security has been particularly tightened around the giant Basilica of San Petronio.
The church has been the subject of several jihadist plots in the past because it contains a 15th century fresco by the artist Giovanni da Modena which depicts the prophet Mohammed being tortured in hell.
Italy's terror-prevention strategy in recent years has involved the deployment of more than 6,000 troops on public security duties, enhanced surveillance of the country's Muslim population, including regulation of mosques, and a policy of administrative expulsions for non-nationals deemed a security threat because of extremist sympathies.
The total number of such expulsions rose to 202 since the start of 2015 with the deportations, announced on Saturday, of two Moroccans and a Syrian.
Three Italians were among the 13 people who were killed in the van rampage in Barcelona on Thursday and 43 Italians have died in jihadist attacks around the world since the 2003 Casablanca suicide bombings.