French Prime Minister Manuel Valls on Wednesday unveils new security measures, including more agents and strict policing of social media. (Pool photo by Philippe Wojazer/European Pressphoto Agency)

Two weeks after the worst attacks on French soil in decades, leaders here announced sweeping measures Wednesday to add more than 2,600 counterterrorism agents and sharply boost funding for intelligence gathering.

The proposals would bolster the capabilities of authorities who already have some of the most extensive counterterrorism powers in Europe, and came as the continent has struggled with a sense of a sharply growing threat from returnees from Islamist conflicts in Syria, Iraq and Yemen. In recent weeks, countries across Europe have detained people they suspect are connected to several alleged attack plots.

Other countries, such as neighboring Belgium, have also said that they would strengthen anti-terrorism forces. There is a rising debate within Europe about whether to build new crime-fighting databases that privacy advocates have long derided as needlessly invasive.

The plan outlined by French Prime Minister Manuel Valls came the same day that French authorities acknowledged that they had intercepted one of the three killers, Amedy Coulibaly, at a routine traffic stop days before the attacks started, but had let him go immediately after. The revelation, first reported by weekly satirical and investigative newspaper Le Canard enchaîné, was sure to raise additional questions about intelligence failures ahead of the attacks. Counterterrorism authorities had extensive contact with all three men, it reported, but determined that they did not pose an immediate threat.

France’s plans do not signal a fundamental change in the country’s counterterrorism strategy. But they do reflect a growing belief in the West and among allies that security forces need to keep pace with evolving terrorist networks that could increasingly include native-born radicals.

The three gunmen suspected of leading the terror campaign were born and raised in France. A total of 17 people were killed in the attacks, which began at satirical newspaper Charlie Hebdo. The gunmen were later killed in simultaneous raids.

“The number of dangerous individuals who might actually launch attacks has been relentlessly increasing in France,” Valls said in a nationally televised address. “This change of scale is a formidable challenge for our country and for our partners, particularly our European partners.”

He said a French counterterrorism registry would be expanded to include about 3,000 people who had been involved in Islamist fighting in Syria and Iraq or were otherwise deemed at risk of radicalization. They will be required to check in closely with security forces about their movements and activities.

Valls said 2,680 new security posts would be created as part of the $493 million effort, which includes providing more tools and technology for monitoring, such as phone-tapping and Internet surveillance.

“This effort is absolutely massive, but it is a prerequisite if we are to ensure the safety of the French,” he said.

Lawmakers involved in drafting the law said Wednesday that they are proposing to give French authorities the ability to track the cars of suspects, force foreign social networks to hand over data directly to them and raise the number of warrantless wiretaps currently permitted under French law.

The announcement came as French prosecutors said they had charged four men in relation to Coulibaly’s portion of the attacks that paralyzed the country.

The men are accused of helping him with logistics and weaponry in the shooting of a police officer and a later hostage-taking at a Paris kosher supermarket, which left four people dead.

It was not clear whether the men — three of whom have long criminal records — were connected to the militant ideology behind the attacks or whether they had simply assisted, said Paris Prosecutor Francois Molins.

“We will probably have months of investigation, if not years,” he said.

He outlined a web of connections between the men and Coulibaly, in whose bathroom was found a suitcase stuffed with jihadist materials and a photocopy of a jihadist flag. In line with French law, the men, ages 22 to 28, were identified only as Willy P., Christophe R., Tonino G. and Mickael A.

Molins acknowledged that police had stopped Coulibaly and his common-law wife, Hayat Boumeddiene, in a routine traffic stop Dec. 30 near the Buttes-Chaumont park in Paris where, more than a decade earlier, a jihadist group that included the other attackers did its exercises before some of them went off to fight in Iraq.

When they checked Coulibaly’s name in their database, the police saw that he had been flagged by intelligence officials as “considered dangerous and taking part in the Islamist movement,” Le Canard enchaîné reported. Coulibaly was driving a rental car, and he showed police a driver’s permit dated Dec. 10. Police were to obtain “a maximum of information without drawing the attention of the subject.” The police notified counterterrorism authorities, who did nothing, the newspaper reported.

France repeatedly has strengthened its counterterrorism laws in recent years, including measures seeking to block French citizens from joining fighters abroad.

Other nations have taken similar steps.

Last week, Belgium’s Prime Minister, Charles Michel, said an additional $348 million would be earmarked for strengthening security. He also proposed a range of policies that include making it easier to strip citizenship from Belgians who fight in Syria and elsewhere.

The tougher measures followed a series of raids in Belgium and other countries against suspected terrorist cells plotting attacks against police and other targets. Authorities do not believe there were direct links to the Paris attacks.