European counterterrorism agencies are scrambling to assess the potential terrorism threats after the arrests of more than two dozen people with suspected links to Islamic extremists.
As many as 20 sleeper cells of between 120 and 180 people could be ready to strike in France, Germany, Belgium and the Netherlands, a Western intelligence source told CNN.
European Union and Middle East intelligence agencies identified an “imminent threat” to Belgium, and possibly to the Netherlands, the source told CNN.
Belgium: Deadly raid
A raid on a Belgium terror cell on the brink of carrying out an attack left two suspects dead Thursday, Belgian authorities said.
A third suspect was injured and taken into custody in the operation at a building in the eastern city of Verviers.
Belgian federal prosecutor Eric Van der Sypt said 13 people were arrested in a dozen ensuing anti-terror raids.
“There is a tremendous amount of concern over sleeper cells in Europe,” said a Western official with direct knowledge of the situation.
Overall, authorities made 17 arrests related to the Belgium threat — 13 in Belgium and four at two locations in France.
The suspected terror cell, which included people returning from Syria, planned to target police officers, Van der Sypt said. Police said they recovered weapons, bomb-making materials and police uniforms.
Sectarian turmoil in Yemen is bolstering al Qaeda in the Arabian Peninsula’s (AQAP) local recruitment, and buying it space for attacks against the West, according to one Western diplomat.
Following up on Paris attacks
European counterterrorism agencies have been trying to identify and thwart potential threats after the deadly attacks in Paris last week, in which 17 people were killed.
The attacks last week started when two gunmen raided Charlie Hebdo magazine, killing 12 people.
A day later, gunman Amedy Coulibaly shot a policewoman in the south of Paris.
Coulibaly killed four more people he had held hostage at a kosher supermarket. Police later shot him and the gunmen in the magazine attack, brothers Said and Cherif Kouachi.
Security officials are working to track those with links with the three attackers.
Ties to militants
Officials are monitoring groups of men who have returned from fighting in Syria.
It is believed ISIS directed men to return to Europe to launch attacks in retaliation for airstrikes against the terror group in Syria and Iraq, according to the official.
Several European nations, including the United Kingdom, France, Belgium and the Netherlands, are participating in the air campaign against ISIS in Iraq.
ISIS runs large training facilities in Syria, has deep financial pockets, and access to thousands of potential European recruits.