Italian police arrested a Tunisian and Pakistani on Wednesday on suspicion they were plotting attacks in Italy and circulating threatening messages on the Internet in support of Islamic State.
The men were arrested in Brescia, a small city near Milan, police said in a statement, without naming either man.
It said the Tunisian man, 35, had created a Twitter account from which he posted "threatening messages signed Islamic State" with the backdrop of famous landmarks such as Rome's Colosseum and Milan's cathedral.
Police were due to give details at a news conference later on Wednesday.
Italian security forces have for months been on high alert against attacks at embassies, synagogues, churches, the Vatican and areas usually crowded with tourists.