Hans-Georg Maassen, Germany's domestic intelligence chief, warned on Sunday that many of the wives and children of German "Islamic State" (IS) fighters "identify deeply" with jihadism and would pose a major security risk if they return home.

In an interview with the Deutsche Presse Agentur (dpa) news agency, the head of Germany's Office for the Protection of the Constitution (BfV) said that although there has not been a major wave of Germans with IS-ties returning home, it was crucial to have security procedures in place.

"There are children who have been brainwashed and highly radicalized at 'schools' in IS-held areas," Maassen said. "It's a problem for us because many of these kids and teenagers can sometimes be dangerous.

Read more: Germany's domestic intelligence agency warns of 'IS' sympathizers

Regarding the repatriation of women from IS-held areas, the BfV chief warned that many "had become so radicalized and identify so deeply with IS-ideology that, by all accounts, they must also be identified as jihadis."

This didn't mean repatriated women would be prepared to carry out terror attacks on German soil, Maassen stressed, but "nevertheless, we have to keep them in our sights."

Maassen's remarks followed reports in the German media last week that the government was exploring plans to repatriate the children of German (IS) fighters.

German jihadis - by the numbers

The German government estimates that around 700 Islamists live in Germany who currently pose a significant security risk, meaning they would be prepared to carry out a terrorist attack. Maassen indicated that among them are several women, although he could not provide a specific number.

Since IS seized territory across Iraq and Syria in 2014, around 950 German jihadi-sympathizers have traveled to the Middle East to fight on behalf of the Sunni militant group. Around 20 percent of them are female.

But as IS continues to suffer major military setbacks and territory losses, the rate of German jihadis returning home is expected to increase. Around one-third of the 950 Germans who traveled to fight for IS have since returned, most of them women are children.

"We haven't seen any significant flows of male fighters returning home," Maassen said. "We assume that Westerners still fighting with IS to this day, intend to stay there until the very end, and will only then seek to settle in Europe once again."

From the Middle East to the home and online front

Although IS is on the brink of military defeat in the Middle East, having effectively lost all its seized territories bar a handful of desert pockets on the Iraq-Syria border, Maassen warned that the war on radical Islam was far from over.

Despite having fewer fighters on the ground, the jihadi group has become what the domestic intelligence chief describes as a "global cyber caliphate."

Read more: EU introduces new measures to combat 'low-tech' terrorism

Those warnings were echoed on Sunday by the president of Germany's Federal Criminal Police Office, Holger Münch.

"We have seen in recent years that the so-called Islamic State is very adaptable," he told German public broadcaster Deutschlandfunk, adding that jihadi online networks were long established and had proven particularly difficult for authorities to control.

Münch added that, in addition to Germany's intelligence services, police authorities were also preparing operations on how they would monitor a significant wave of Germans returning from IS-held territories.

Maassen also warned of an uptake of IS propaganda in European countries that tells potential militants to take the fight to their own countries.

"They are saying: 'You don't have to travel to Syria and Iraq to fight. You can carry out jihad at home, as well,'" Maassen told dpa. "Therefore, many of those who had already packed their suitcases to travel to these jihadi territories decided to stay at home instead."