Italy is looking for five terror suspects after a tip-off from the United States about possible jihadist attacks on tourist sites in Rome and Milan, Italian Foreign Minister Paolo Gentiloni said.
The US embassy in Rome posted a security warning on its website identifying some of Italy's best-loved landmarks as "potential targets", including St Peter's Square, La Scala and the Duomo cathedral in Milan.
It also said churches, synagogues, restaurants, theatres, and hotels in both cities could be targeted.
"Terrorist groups may possibly utilise similar methods used in the recent Paris attacks," it added.
The US Federal Bureau of Investigation (FBI) had provided five names to the Italian authorities but the agency did not give specific details on any plots, according to Italian media.
"Since yesterday afternoon, our security forces have been working to find five people," Gentiloni told Rai 3 television, without elaborating.
He added that Italy was already primed for the possibility of an attack.
"The minister of the interior has explained many times that we are at a very high level of alert covering symbolic sites, places where people gather, from stadiums to cathedrals, and St Peter's in particular, which were, among others, the places highlighted by the FBI," Gentiloni said.
"We always take such signals of alarm very seriously, especially when they come from the United States."
He stressed that the US warnings did not amount to formal advice to Americans not to travel to Italy – a step which would have serious repercussions for the country's large tourist industry – but a simple reminder of the need to be vigilant.
He also appealed to the media not to stoke public fears.
"We must not become prisoners of this alarm because that would be a gift to Daesh," he said, using an acronym for the Islamic State group.
Meanwhile, local media reported that Italian police had arrested two Syrians trying to travel to Malta on false passports who had pictures related to the Islamic State jihadist group on their phones.
The two men, aged 19 and 30, were apprehended at Bergamo airport near Milan late on Wednesday (local time) after presenting Austrian and Norwegian passports but answering only to Arabic, the Eco di Bergamo daily said.
They had been trying to board a flight to Malta. Security officials who searched their mobile phones found photographs related to the jihadist IS group, it said.