The warning came as more than 50,000 people sought political asylum in Europe in 2014, a 44 percent hike over the previous year. Twenty percent of those applicants were Syrians, the Eurostat agency said. Seven thousand asylum seekers were granted refuge in Austria alone.
"We must be vigilant. It is relatively easy to enter into the European Union when one joins an influx of refugees," de Kerchove said on the sidelines of a ministerial meeting in Vienna.
De Kerchove, a Belgian, said although Europe was currently being targeted for attacks by individuals claiming to act on behalf of Islamic State, it was also not safe from attacks by Al-Qaeda seeking to "show that they are still out there."