"We must therefore assume that we will also be targeted by terrorist attacks, and we must adapt," said Maassen, adding that around 70 of those returnees are suspected of having committed serious offences and acts of war.
"Round-the-clock observation is hardly possible," warned the security chief of the practical difficulties of preventing individuals from carrying out attacks, but added that there were no indications of particular plans for an attack.
Terror groups such as the Islamic State and al-Qaeda want to destabilize the West by spreading terror and fear through their terrorist attacks, said Maassen, and seek to sustain the ideology of global jihad in German and European cities.
Tagesschau.de reports that of the estimated 600 German citizens who have traveled to conflict zones in the Middle East, around 70 are believed to now be dead, with tens of thought believed to have carried out suicide bombings. In mid-January, the German Interior Ministry gave a figure of 150-180 jihadi returnees to Germany.