Speaking to the "Neue Osnabrucker Zeitung," Europol Director Rob Wainwright said "Islamic State" terrorists were planning new attacks on the continent, DW wrote.

"One can expect IS or other religious terror groups to stage an attack somewhere in Europe with the aim of achieving many casualties among the civilian population," Wainwright said. Not only groups of militants, but also individuals could be expected to carry out strikes, he added.

Wainwright spoke shortly after a terror strike in Ankara killed 28 people.

According to the Europol, between 3,000 and 5,000 Europeans have returned to Europe after being trained in terror camps. "The growing number of these foreign fighters presents new challenges for EU countries," the Europol head said.

However, the attackers were not coming with refugees currently making their way into Europe, according to Wainwright.

"There are no concrete indications that terrorists are systematically using the stream of refugees to come into Europe undetected," Wainwright told the "Neue Osnabrucker Zeitung."

EU security forces have been on alert since militants simultaneously attacked a concert hall, a football stadium, cafes and bars in Paris on November 13, 2015. Those attacks killed 130 people and many others were injured.

EU officials created the European Counter Terrorism Center (ECTC) earlier this year to boost cooperation among intelligence agencies of member states and aid them in their fight against terror.