The European Union police agency Europol has warned that Islamic State is likely to launch more attacks in Europe, with several dozen militants already in place.

In a report on the threat the Islamist group poses to EU countries, Europol says the most probable forms of attack would be cyber attacks, mass shootings, suicide bombings and other assaults by radicals acting alone.

The agency stresses that EU countries should take strict precautions against elaborate attacks and strengthen cooperation and information exchange.

Europol also points out that more Europeans who join ISIL could return to Europe as the group faces setbacks in Syria and Iraq.