The head of the European Union’s police agency, Europol, warned on Friday that the large number of radicalised Islamic extremists across Europe, their lack of command structure and growing sophistication make it “extremely difficult” for law enforcement agencies to foil every terror attack. The US news outlet quoted a separate western intelligence source as saying that the ongoing terror threat in Europe involved up to 20 sleeper cells of between 120 to 180 people ready to strike in France, Germany, Belgium and the Netherlands. A senior Belgian counter-terrorism official, who was not named, told CNN that the alleged terror cell was believed to have received instructions from Islamic State. Police sources told Belgian television stations they had resolved to launch the pre-emptive operation against the terrorist suspects a fortnight ago after bugging the homes and cars of the men who were said to have recently returned from fighting in the war in Syria. Counter-terror officers kill two and arrest 15 suspected jihadis in Belgium and France with Europe on high alert for further attacks 
 
 A major Islamist plot to kill police officers in the street has been foiled at the eleventh hour, prosecutors have said, after counter-terror raids led to the arrest of 15 suspected jihadis in Belgium and France. Eric van der Sypt, a Belgian federal magistrate, said 13 suspected terrorists were arrested in Belgium overnight with a further two detained in France. French and German authorities arrested at least 14 other people on Friday suspected of links to Islamic State (Isis), and the Gare de l’Est train station in Paris was evacuated after a bomb scare, with Europe on high alert for further potential terrorist attacks. • The suspected terror cell, which included people returning from Syria, planned to target police officers, Van der Sypt said. Photograph: Paul Zinken/Corbis 
 
 Separately, on Friday morning police in Berlin arrested two men suspected of helping to recruit for Isis in Syria. Police said the men were not suspected of planning attacks in Germany. The Paris prosecutor’s office said 12 people were arrested in anti-terrorism raids in the region, targeting people linked to the gunman who attacked a kosher supermarket in the wake of the Charlie Hebdo killings and claimed ties to Isis.
– Yesterday's terror raids in Belgium stopped, at the last minute, a terrorist plan to kill police officers in the street, officials say. Two suspected terrorists were shot dead in the series of raids, and another 15 were arrested in Belgium and France, the Guardian reports. Authorities were working to take down what they say was an active terror cell rooted in the two countries; the two gunmen killed in Verviers—and a third one who was wounded and among those detained—are believed to have been part of a "homegrown cell of jihadists" just recently back in Europe from Syria. Police found ammo, weapons including explosives, police uniforms, communication devices, and cash; they say the terrorists' plan also targeted buildings in Belgium, and several Jewish schools have been closed after warnings they could be targets. More: The Gare de l’Est train station in Paris was also evacuated after a bomb scare today, and Europe is on high alert for potential attacks. Officials say there is no link between the Belgium raids and last week's Paris terror attacks, but one notes that "a second potential Paris has been averted" with these raids. (Another 10 suspected terrorists allegedly linked to the Charlie Hebdo attacks were arrested in Paris today.) A Western intelligence source tells CNN that as many as 180 people in as many as 20 sleeper cells are primed to attack France, Germany, Belgium, and the Netherlands. And European security services have gotten tips that ISIS may be telling Europeans who have joined up in Syria and Iraq to launch attacks on their home soil; security agencies are investigating people recently returned from those countries. Separately, Germany arrested three men suspected of being involved with ISIS, but none appear to have been planning attacks.