Europol has warned that terrorists from Islamic State (IS) will aim to step up attacks on European targets, as they face defeat in the Middle East. <br/><br/>European police force says more foreign fighters will try to come back to Europe, and several dozen capable of attacks could already be there. <br/><br/>Their tactics could include car bombs, kidnappings and extortion, it said. But the report plays down the likelihood of attacks on critical infrastructure, such as nuclear sites. Europe has been shaken by a series of attacks in recent years blamed on IS terrorists.