Europe is facing the threat of an al-Qaeda terror attack.
Western intelligence says there is a high risk of a strike by so-called homegrown militants.
British and American security services believe France and Germany are likely targets.
Gilles de Kerchove, the EU’s counter-terrorism coordinator, said homegrown jihadist movements are the most worrying development in the fight against extremism.
“People living in Europe who might already have an EU passport and so they can slip under the radar,” de Kerchove said.
The question then for European officials: how best to deal with them?
“We need to decide if Europe should create a continent-wide database to collect information on passengers. Many say this new menace must be fought with new tools,” he added.
European governments say the threat is very real and warn travellers to be vigilant in tourist hotspots.
US media reports have suggested militants are plotting to attack some of the continent’s famous landmarks including the Eiffel Tower in Paris and Berlin’s Brandenburg Gate.
The alleged plot has drawn comparisons with the 2008 Mumbai attacks in India that killed 166 people.