BERLIN—The head of Germany’s domestic intelligence agency is warning that more terror attacks by Islamic extremists in Germany are likely.

Hans-Georg Maassen said Tuesday that “further attacks by single persons or terror commando groups must be expected.” He and German Interior Minister Thomas de Maiziere were presenting the annual report by Germany’s domestic intelligence agency.

De Maiziere told reporters some 680 extremists are considered potentially dangerous enough to carry out an attack.

Although Tunisian Anis Amri had been under surveillance, he was able to hijack a truck in December and drive it into a crowded Christmas market in Berlin, killing 12 people and wounding dozens — the first mass-casualty Islamic extremist attack in Germany.

Maassen says 10,000 people in Germany are part of the radical Islamic Salafist scene but not all are violent.

Read more about: