BRUSSELS: It is impossible to completely prevent new Islamist attacks like those in Paris, the EU's anti-terror chief said Tuesday, warning that Europe's prisons have become a “massive incubator” for radicalisation.

Gilles de Kerchove told AFP in an interview that the Islamic State group and Al-Qaeda wanted to launch more attacks on the West like the assault on the French capital last week in which 17 people were killed over three says.

“We can't prevent (militant attacks) 100 per cent,” said de Kerchove, who met with European, US and Canadian security ministers in Paris on Sunday in the wake of the Charlie Hebdo massacre and linked attacks.

“The threat remains serious,” he added.

De Kerchove warned that the Al-Nusra Front, the Al-Qaeda branch in Syria, is also looking for “clean skins,” Europeans with no record of radical activity, to mount attacks in Europe.

EU's anti-terror chief Gilles de Kerchove

He also said that weapons from the Balkans and Libya were being sold in Europe and it was extremely difficult to prevent “crazy people” from obtaining them and carrying out attacks if they wanted to.

“It's a real challenge but one can try to prevent them as much as possible without becoming a totalitarian society,” he said.

Prison 'incubator'

De Kerchove warned that it was better to try to rehabilitate jihadists, including those returning to Europe from Syria and Iraq, than to jail them even if there was “no miracle solution.“

Two of the Paris gunmen - Cherif Kouachi, one of the brothers who massacred 12 people in an attack on the offices of the Charlie Hebdo magazine, and Amedy Coulibaly, the Islamist who killed four hostages at a Jewish supermarket in Paris last week, were both believed to be have been radicalised in prison.

Both Mohamed Merah, the Al-Qaeda militant who shot dead seven people in a series of 2012 attacks, and Mehdi Nemmouche, last year's Brussels Jewish museum killer, were also radicalised in jail.

“We know that prisons are a massive incubator for radicalisation,” the counter-terror chief said. "We must work more on (stopping) radicalisation in prison. I know things are being done, but insufficiently."

The problem had become so great that he recommended “not sending all those who return from Syria to prison” because they will inspire other inmates with tales of heroism.

Around 3,000 European citizens had joined the jihadist cause in Syria and Iraq with around 30 percent have returned to their EU countries, De Kerchove said in September.

“We must remain very, very vigilant,” he added Tuesday.

Air travel database

De Kerchove said it was more important than ever to establish a European Union-wide database of passenger travel information, provided that information protection laws were respected.

Such a system would allow EU members to collect and share data on all airline passengers in a bid to trace would-be militants -- a move critics say infringes on civil liberties.

He said the risk now is that many of the 28 EU member states will establish their own PNR, which will be less effective than one involving all of them.

On a positive note, De Kerchove said the social media campaign launched after the attacks on the Charlie Hebdo magazine in Paris last week may prove to be a counterpoint to the propaganda jihadists used to recruit others.