Germany's top domestic intelligence official says brutal videos produced by the Islamic State group and others are part of a "psychological warfare" effort.

Hans-Georg Maassen says countries need to counter the effect that slickly produced propaganda has on young people by highlighting the "gruesome reality" of life under IS.

The group recently released a video calling on its followers in Germany to carry out attacks such as those seen in France in January. German security officials say the video was voiced by Berlin-born extremist Denis Cuspert, who was designated as a global terrorist by the United States in February for fighting for IS.

Maassen said Wednesday that some 680 Islamic extremists have traveled to Syria and Iraq in recent years. About a third have returned to Germany.