The suspected key link between senior ISIS operatives in Syria and the Belgian terrorist cell, Belgian-Moroccan ISIS fighter Abdelhamid Abaaoud, is still at large, a senior Belgian counterterrorism official said.
Abaaoud's last known location was believed to be Greece, the official said.
As Belgium's search continues, other European nations are also moving in on suspected Islamist cells amid concerns heightened by the terror attacks in Paris two weeks ago.
Here's a look at the latest developments: -
Police in Berlin, Brandenburg and Thuringen raided 13 properties linked to suspected radical Islamists overnight, police in the German capital said Tuesday.
Most of the action was directed at a group connected to a mosque in the district of Berlin-Moabit.
The overnight raids are part of the investigation into two alleged Islamists who were arrested Friday, identified as Ismet D. and Emin F., Berlin police said. Both of them are accused of providing logistical aid to ISIS.
Some 200 police officers were involved in the raids at 13 sites across three German states. Those subject to the raids have not yet been accused of any crimes, but had contact with Ismet D. and Emin F.
There are no indications that the group was preparing attacks in Germany.
Five Belgian nationals have been charged with participation in a terrorist organization in connection with last week's raids, federal prosecutor Eric Van Der Sypt said. The terror cell was on the brink of an attack and planned to target police officers, he said.
Belgian counterterrorism agencies say they suspect that the ringleader of the cell is Abaaoud, the senior Belgian counterterrorism official said.
Abaaoud is also known as Abou Omar Soussi and Abou Omar al Belgiki, the official said.
According to Guy Van Vlierden, a reporter at the Belgian newspaper HLN who tracks Belgian foreign fighters in Syria for the blog "emmejihad," Abaaoud is a 27-year-old from the Molenbeek district of Brussels who traveled to Syria in January 2014 and joined ISIS soon afterward.
The two gunmen killed in one of the raids, in the city of Verviers, are Belgians of North African descent from the same Brussels district. They were in phone contact with an ISIS ringleader in Greece, who Belgian authorities believe was probably Abaaoud.
But Belgian authorities have not ruled out the possibility that an Algerian suspect arrested in Greece over the weekend was the key link between the terror cell and ISIS. That 33-year-old suspect was wanted in Belgium on charges of terrorist activity, Greek police said Monday. Belgium is requesting an extradition.
One suspect survived the police raid in Verviers, named as Marouane El Bali. He was taken into custody and faces charges of participation in a terrorist organization and possession of explosives with intent to commit a criminal attack, among other charges, said his attorney, Didier De Quevy.
But De Quevy said his client was not involved in any terrorism; he was just delivering shoes to a friend when he was caught in the wrong place at the wrong time.
Five men -- purportedly Russians of Chechen origin -- were arrested in southern France overnight while planning an act of terrorism, according to French media reports Tuesday.
A cache of explosives was found, according to Midi Libre and other media outlets, quoting police sources and the local prosecutor, Yvon Calvet. CNN has not yet been able to confirm the reports.
Meanwhile, the Paris prosecutor's office said Tuesday that four men arrested Friday are being placed under criminal investigation in connection with the Paris terror attacks.
They are under investigation for association with a criminal terrorist organization with the objective of committing crimes against people.
In addition, one of those in custody will be under formal investigation for possession or transport of weapons linked to a terrorist enterprise.
The four men, ages 22, 25, 26 and 28, will remain in custody. Five other suspects held since Friday were released Monday night.
Investigators say DNA found in a car used to transport Jewish market attack gunman Amedy Coulibaly has been traced to a man who is already in custody in connection with the attacks, according to a source familiar with the ongoing investigation.
Investigators are still looking for a person whose DNA was found on a magazine for Coulibaly's gun.
Coulibaly killed four hostages on January 9 at a kosher grocery store in Paris before police killed him. He's also believed to have killed a policewoman a day earlier. Before the siege, he had proclaimed his allegiance to the Islamic State in Iraq and Syria
, or ISIS.
New surveillance video obtained by CNN shows Coulibaly and his partner Hayat Boumedienne outside a Jewish institution in Paris. The video was recorded at the end of August or beginning of September and stored on a security camera.
A source familiar with the ongoing investigation into the Paris attacks says the nature of the video makes it clear that the couple was carrying out surveillance of possible targets for several months before Coulibaly launched his attack against the kosher supermarket.
New York Mayor Bill de Blasio visited the scene of the siege Tuesday, and he added flowers to a mound of bouquets, candles and handwritten tributes to those killed. He voiced his solidarity with France as it combats terrorism, and he met with representatives of the Jewish community.
The supermarket assault happened during three days of terror in Paris that began with the January 7 attack on offices of the Charlie Hebdo satirical newspaper by gunmen Said and Cherif Kouachi.
In all, 12 people died in the Charlie Hebdo attack. The funeral for maintenance worker Frederic Boisseau, the first person to be killed, took place Tuesday.
Al Qaeda in the Arabian Peninsula, al Qaeda's Yemen affiliate, claimed responsibility for the Charlie Hebdo shootings.
France's Le Monde newspaper suffered a different kind of attack on Tuesday, when its official Twitter account was apparently hacked by the Syrian Electronic Army, a group of pro-Syrian regime hackers that has aggressively targeted major news organizations and activists. One post that appeared on the newspaper's Twitter account said, "Je ne suis pas Charlie" ("I am not Charlie") and decried attacks on Syria.
"After the hacking of our account, our teams have taken it back into our hands," the newspaper's account said in another tweet about an hour later. "We apologize for any fraudulent posts on our behalf."