Five people, including at least one Islamist radical, have been arrested after an improvised bomb was found in a quiet street in one of the most expensive residential districts of Paris.
"When you watch someone, there is always a nebula, a friend ready to help the one who is on the file", Mr Collomb told France Inter radio station.
In Saturday's incident, a resident alerted police after finding two gas cylinders about 4:30am in his building in the Porte d'Auteuil neighbourhood, a source close to the probe said.
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France's interior minister Gerard Collomb said the discovery of the device in western Paris highlighted that France was as much as ever at risk of terrorist attacks.
Investigations are entrusted to counter-terrorism section of Criminal Brigade of Paris Police prefecture and to Directorate-General for Homeland Security (ITSB).
"We've foiled numerous attacks since the start of the year that would have involved many deaths", the minister said.
The terrorist threat remains high in France affected since January 2015 by a series of jihadist attacks that made 239 dead. Although the so-called "Islamic State" group claimed the attack, the man's motives are still unclear.