Italian police have arrested a 24-year man found in possession of explosive materials after the FBI flagged him as a possible extremist.

Police in the central Italian city of Viterbo said Thursday that they searched the man's house after the FBI informed them that he had praised on social media the 2017 truck attack on a cycling path in New York City that killed eight people.

The suspect, whose name has not been released, was arrested for possession of explosive substances while authorities investigate other possible charges. Police also seized two air pistols.

Police spokesman Fabio Berrilli told SKY News24 that the suspect "could be dangerous," but there was no indication he was planning imminent attacks and the only sign of radicalization were statements praising the New York attack.