Police blocked off roads early Wednesday in Saint-Denis, which is home to the Stade de France sports stadium where three suicide bombings took place Friday.
French police wouldn't comment on whether any officers had been shot in the Saint-Denis operation.
BFMTV reported that the police raid was linked to the hunt for the so-called "ninth suspect," who may appear in a video recorded by a witness to the attacks.
Police have been analyzing the video, which shows two gunmen inside a black car linked to the attacks and perhaps a third individual driving the car, French media reported.
Seven of the attackers were killed during the wave of violence Friday night, and an international arrest warrant is already out for one suspect, Salah Abdeslam
, a 26-year-old Frenchman. The identity of the possible ninth suspect is unknown.
Brother urges suspect to surrender
Abdeslam's older brother has urged the suspect, who was last seen driving toward the Belgian border hours after the attacks, to turn himself over to authorities.
"I would tell him to surrender. That's the best solution," Mohamed Abdeslam told CNN's Erin Burnett on Tuesday. "But of course, if he has something to do with it, he must accept responsibility."
In their push to unravel the attack plot and the suspected network behind it, counterterrorism and intelligence officials say investigators have uncovered a clue that could be a big break: cell phones believed to belong to the attackers.
According to the officials, one of the phones contained a message, sent sometime before the attacks began, to the effect of: OK, we're ready.
"It points to a sort of organization," CNN terrorism analyst Paul Cruickshank said, "an attempt to try to synchronize what was going down."
But cracking into their communication won't be easy.
Investigators have found encrypted apps on the phones, which appear to have left no trace of messages or any indication of who would have been receiving them, according to officials briefed on the French investigation.
'These are not regular people'
Mohamed Abdeslam said the last time he saw his brothers was about a week ago.
"They left without saying goodbye," he said.
Now one of them is a wanted fugitive. And authorities say another Abdeslam brother, Ibrahim, 31, was among the seven terrorists who either killed themselves or were killed by police in a series of coordinated attacks across the French capital on Friday night that killed at least 129 people and wounded hundreds more.
Mohamed Abdeslam told CNN that before the attacks, he'd noticed his brothers changing and adopting more radical views. He suspects the Internet could have played a role. But he said his family was shocked by the attack, and had no idea what they were planning.
"My brother who participated in this terrorist act must have been psychologically ready to commit such an act. These are not regular people," he said. "You cannot have the slightest doubt that they have been prepared, that they must not leave any trace which would cause suspicion that they might do such things. And even if you saw them every day, their behavior was quite normal."
Suspects questioned by Belgian authorities in February
Police stopped Salah Abdeslam hours after the attacks in a car on his way toward the Belgian border. They let him go because he apparently hadn't yet been linked to the terrorist operation.
Both he and Ibrahim were previously known to authorities: Belgian prosecutor Eric Van Der Sypt told CNN's Ivan Watson that police questioned the Abdeslam brothers in February.
"Ibrahim tried to go to Syria and was sent back by the Turks in the beginning of 2015," Van Der Sypt said. "It was after that that we questioned him."
Both brothers were released, the federal prosecutor said, after they denied wanting to go to Syria.
He said Belgian authorities were also trying to keep an eye on Bilal Hadfi, one of the suicide bombers who struck outside the Stade de France, according to several sources. "We knew (Hadfi) was in Syria," Van Der Sypt said. "But what we didn't know is apparently he was back, as he blew himself up in Paris. But we had no knowledge of the fact that he was back in Europe."
'At war' and launching airstrikes
Declaring the country is "at war," French President Francois Hollande has proposed extending the state of emergency
for a further three months, along with sweeping new anti-terrorism laws.
Security forces conducted more than 128 new raids around the country overnight, Interior Minister Bernard Cazeneuve said Tuesday during a radio interview.
Meanwhile, outside the country, French warplanes have launched wave after wave of airstrikes
on ISIS' de facto capital of Raqqa in northern Syria, and a major Belgian police operation was conducted Monday in the Abdeslams' home base in Molenbeek
, a Brussels suburb with a history of links to Islamist terror plots.
Belgian authorities say two men detained over the weekend in Molenbeek in connection with the attacks are now under arrest for "attempted terrorism and participation in the activities of a terrorist group."
Tracking the suspected mastermind
Before the Paris attacks, France and its allies had tried to target a prominent ISIS member who is believed to have planned the assault on the French capital, a French source close to the investigation said.
Western intelligence agencies had attempted to track Abdelhamid Abaaoud
, a Belgian citizen thought to be in Syria, but they weren't able to locate him, the source told CNN on Tuesday.
Abaaoud had been implicated in the planning of a number of terrorist attacks and conspiracies in Western Europe before the Paris attacks.
Believed to be close to ISIS leader Abu Bakr al-Baghdadi, he was linked to a plan to attack Belgian police
that was thwarted in January. He has since been featured in ISIS' online English-language magazine. His current whereabouts are unknown.