Paolo Gentiloni referred to "possible terrorist attacks that could be aimed at St Peter's Basilica in Rome or the Duomo (cathedral) or Scala theater in Milan".
Honduras arrests five Syrians headed to US with stolen passports
"As of yesterday our security forces are working to identify five people," he said in an interview with state broadcaster RAI.
Italy raised its security alert level to 2, the highest possible in the absence of a direct attack on the country, following Friday's attacks in Paris in which Islamic State gunmen and bombers killed 129 people.
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Gentiloni said the US embassy in Rome had recommended tourists take particular care in certain parts of Italy but had not advised them against going there.
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