The suicide bomb belt found is said to resemble belts used by the attackers and was discovered 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, also 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 that the threat remains “imminent”.
The police in Belgium has charged a fourth suspect with terrorism offences related to the deadly attacks on Paris.
This was 10 days after the Islamic State (IS) militant group launched near-simultaneous attacks in Paris that killed about 130 people.
While the French President, Francois Hollande, described the attacks as an ‘act of war’ organised by the militant group, the French Interior Minister, Bernard Cazeneuve, asked European countries to ‘wake up’ to terror threats after it emerged that the suspected Belgian ringleader of the attacks had entered France undetected.