PARIS — France is tracking hundreds of people believed to belong to possible sleeper cells for terror organizations like al-Qaida or the Islamic State group, the country’s top security official said.

In an interview with The Associated Press, Interior Minister Bernard Cazeneuve laid out what has become an increasingly urgent question for European intelligence services: How to trace the moment when someone transforms from a disgruntled criminal or a disaffected citizen into a terrorist, and how to block those first steps toward radicalization.

“Four hundred targets have been identified by our intelligence services that are more or less sleeper cells, affiliated or in relation with al-Qaida-type organizations, that can strike like the Kouachi brothers,” Cazeneuve said in an interview late Monday.

Said and Cherif Kouachi were French-born brothers who killed 12 people in Paris on Jan. 7 when they stormed the satirical newspaper Charlie Hebdo. They were shot dead by police in a confrontation two days later.

Cazeneuve said he wants new measures to give intelligence services more leeway to monitor suspects’ electronic communications. He is heading to the United States on Wednesday to try and persuade Internet giants to step up and help stem extremists’ ability to use propaganda videos to recruit and indoctrinate new followers.

Facebook, Twitter, Apple and Google — all major vectors for increasingly sophisticated jihadi clips targeting potential followers in the West — will be among his stops in Silicon Valley.

“Ninety percent of those who commit terrorist acts fall into it after regularly consulting websites or blogs that call for or provoke terrorism,” Cazeneuve said.

With the news that the suspected gunman in the deadly Copenhagen attacks this weekend may have been radicalized during a series of stints in jail — like at least two of the gunmen in the Paris attacks last month — Cazeneuve’s trip to the U.S. to strengthen intelligence sharing between governments and win over the tech firms takes on added importance.

The pace of foreign fighters joining the Islamic State and other extremist groups has not slowed and at least 3,400 come from Western nations among 20,000 from around the world, U.S. intelligence officials say.

“We won’t be able to deal with this subject by always brushing the dust under the rug,” Cazeneuve said. “At some point the dust gets thicker than the rug.”

The minister said the Kouachi brothers were under French surveillance from 2011 until 2014 after the U.S. government tipped off the French about Said Kouachi’s trip to Yemen, but the monitoring produced nothing that indicated the brothers were on the verge of a deadly attack.

Cherif Kouachi had served time for being part of a jihadi recruiting network and was apparently behind bars when he met the third Paris gunman, Amedy Coulibaly, a small-time criminal who became radicalized in prison. Coulibaly pledged allegiance to the Islamic State group in a posthumously released video that is still circulating among jihadis.

“When you have terrorists who keep a low profile for years and then suddenly decide to act — either to obey an order from large terrorist organization such as al-Qaida or of their own volition — then you need to be able to monitor them on a long term,” the minister said.

Further worrying European officials are the networks of radicals in jail who use their prison terms to influence others behind bars.

“You have a few of them who maintain that religious fanaticism, which very likely didn’t start that way, but they use it to have an excuse to be angry and do all these ugly things,” Kim Oesterbye, head of the Danish Prison Officers Union, told The Associated Press. “If we see people who change toward having more radical behavior, then we can report it.”

In the Danish shootings case, prison officials last year alerted PET, the domestic intelligence agency, to the suspected Danish gunman but the report gave no indication he was planning an attack. Two sources close to the case identified the gunman to the AP as Omar Abdel Hamid El-Hussein but Danish authorities have not yet released his name.

France also is pushing to treat jihadi material on the Internet like child porn, a task that before the attacks in Paris was getting scant traction but now seems to have caught the attention of Europe’s top security officials.

“Everyone agrees now that legislation that prevents the diffusion of child pornography is protecting citizens from crime. It is the same for terrorism,” Cazeneuve said. “Calling for anti-Semitism, calling for crimes, calling for murder, calling for the killing of Jews or journalists — that’s not about freedom of expression. That is a criminal act.”