The head of Germany's domestic intelligence agency has warned of the 'massive danger' posed by returning ' brainwashed' ISIS women and children.

'There are children who have undergone brainwashing in the ISIS areas and are radicalised to a great extent,' said Hans-Georg Maassen.

He said Germany should consider repealing laws restricting surveillance of minors under the age of 14 to prepare for the increased risk of attacks by children as young as nine.

'We see that children who grew up with Islamic State were brainwashed in the schools and the kindergartens of the Islamic State,' he said. 'They were confronted early with the ISIS ideology ... learned to fight, and were in some cases forced to participate in the abuse of prisoners, or even the killing of prisoners.'

The German government says it has evidence that more than 960 people left Germany for Iraq and Syria through November 2017 to fight for the Islamic State, of which about a third are believed to have returned to Germany. Another 150 likely died in combat, according to government data. Pictured: An ISIS fighter walking in Syria in 2014

'There are children who have undergone brainwashing in the ISIS areas and are radicalised to a great extent,' said Hans-Georg Maassen, the head of Germany's domestic intelligence agency. Pictured: ISIS supporters celebrating in Syria in the summer of 2014

The radicalisation of minors has been a big topic in Germany given that three of five Islamist attacks in Germany in 2016 were carried out by minors, and a 12-year-old boy was also detained after trying to bomb a Christmas market in Ludwigshafen. Pictured: Heavily armed police walk through the Breitscheidplatz Christmas market where 12 people were murdered in a truck attack on December 19, 2016

Maassen said ISIS also continued to target vulnerable youths in Germany through the Internet and social media, often providing slick advertising or age-appropriate propaganda to recruit them to join the jihadist group. Pictured: A vigil after the 2016 Berlin attack

Maassen, head of the Office for the protection of the Constitution - Germany's equivalent of MI5 - added: 'We are already observing the return of some women and adolescents. This is a problem for us because these children and adolescents in particular can be a danger.

'We also know that there are women one can rightfully call jihadists after living for years in ISIS areas where they identified strongly with ISIS ideology.

'We have to consider that these children could be living time bombs,' he said. 'There is a danger that these children come back brainwashed with a mission to carry out attacks.'

The radicalisation of minors has been a big topic in Germany given that three of five Islamist attacks in Germany in 2016 were carried out by minors, and a 12-year-old boy was also detained after trying to bomb a Christmas market in Ludwigshafen.

The German government says it has evidence that more than 960 people left Germany for Iraq and Syria through November 2017 to fight for the Islamic State, of which about a third are believed to have returned to Germany. Another 150 likely died in combat, according to government data.

Maassen said ISIS also continued to target vulnerable youths in Germany through the Internet and social media, often providing slick advertising or age-appropriate propaganda to recruit them to join the jihadist group.

'Islamic State uses headhunters who scour the Internet for children that can be approached and tries to radicalise these children, or recruit these children for terrorist attacks,' he said.

He said not all were returning home intent in perpetrating terror but insisted: 'We must keep an eye on these women.'

The intelligence chief added that defeat in the Middle East is by no means the end of ISIS. Pictured: An aerial view of the aftermath of the Berlin attack

A mourner places a candle on December 21, 2016 at a makeshift memorial near the Kaiser-Wilhelm-Gedaechtniskirche in Berlin, close to the site where a truck crashed into a Christmas market two days before

The return exodus comes as ISIS strongholds in both countries fall. So far, however, there has been little sign in Germany of surviving male fighters coming back. Pictured: ISIS fighters posing with a Koran, weapons and a flag

Germany lost around 1,000 of its citizens to the Islamic State cause in Iraq and Syria, Europe as a whole an estimated ten to 15,000.

The return exodus comes as ISIS strongholds in both countries fall. So far, however, there has been little sign in Germany of surviving male fighters coming back.

'As far as the fighters are concerned, we do not yet see a strong return movement,' said Maassen.

'We are assuming that those from the West who are still struggling at the moment will want to be there until the end – and only then a movement to return to Europe will start.'

He warned not only Western fighters, but also other jihadists, would try to come to Europe.

The intelligence chief added that defeat in the Middle East is by no means its end.

He added: 'The geographical demise of ISIS in Syria and Iraq does not lead to the disappearance of the terrorist militia. ISIS is now represented in some other states and is quite strong there. In addition, the group is networking enormously in virtual space. There's a global cyber-caliphate.

'It sends the message to its followers: "You don't necessarily have to come to Syria and Iraq to fight. You can also lead jihad where you are".

'Many who sat on packed suitcases and wanted to travel to jihad have therefore remained in their homeland.'

He warned that there is a risk that this group will commit terrorist acts in European cities.