French police are examining what appears to be a suicide bomb belt dumped on a Paris street, 10 days after the attacks that killed 130 people, the BBC reports.
It is said to resemble belts used by the attackers and was found in a suburb which a suspect is thought to have passed through after the attacks.
The US has issued a worldwide travel alert in response to the attacks.
The Belgian capital Brussels remains on high alert, and schools and the metro will stay closed on Tuesday.
They are due to reopen on Wednesday but the highest alert level will continue for at least another week.
Authorities fear Paris-style attacks may be carried out in the city, where at least one Paris attacker lived, with Prime Minister Charles Michel warning the threat remained “imminent”.