Asylum seekers must be taught that Germany has zero tolerance for sex crimes, its migration commissioner said, following outrage over the rape of an 18-year-old woman that led to the arrest of seven Syrians.

All asylum seekers must receive signposting courses on co-existence in Germany as soon as they arrive in the country, or at the initial reception centre, and that includes zero tolerance for sexual abuse and other acts of violence,' said Annette Widmann-Mauz, minister of state for migration, refugees and integration.

'Men who have been living here for a long time need to talk clearly about sexuality and equal rights in Germany to men who have just arrived — if necessary in their native language,' she added.

'The perpetrators must be brought before a court and punished severely,' Ms Widmann-Mauz told the RND news organisation.

Annette Widmann-Mauz, Germany's minister of state for migration, refugees and integration (left), with Chancellor Angela Merkel, has demanded that migrants be taught about the country's zero tolerance towards sex crimes as soon as the arrive in the country

In her role as minister of state for migration, Widmann-Mauz works in the chancellery under Chancellor Angela Merkel.

German police arrested the seven Syrian men, aged 19 to 29, along with a 25-year-old German man last month on suspicion of raping the woman in the southwestern town of Freiburg.

One of the suspects, identified only as 21-year-old Majd H., allegedly orchestrated the rape of the teenage girl.

German newspaper BILD reported that an arrest warrant for the suspect, who was known to police and had a prior conviction for assault, had been issued on October 10.

According to BILD, the warrant clearly noted how dangerous Majd H is and categorized him as a multiple offender.

The picturesque centre of the historic city of Freiburg has been the scene of clashes between far right and hard left protesters following the gang-rape of an 18-year-old girl

It went on to say that there was a high probability he might commit other significant, similar offenses, including grievous bodily harm, sexual coercion and exhibitionism.

Finally, it issued a stark warning: To prevent worse, arrest him urgently.

Another man is suspected of drugging the woman's drink in a Freiburg nightclub before they all took turns at sexually assaulting her in a thicket outside.

The crime has shocked Freiburg, a picturesque university town, and risks stirring up anti-refugee sentiment across the country as the anti-immigration Alternative for Germany (AfD) seeks to cement itself as the leading opposition party.

The AfD's rise is attributed in part to a public backlash against the arrival of more than a million migrants since mid-2014, many of them from Middle East conflict zones.

Alleged chief suspect Majd H., 21, poses in his homeland with a large machine gun, his father told local media his son became 'more aggressive' after they fled the Syrian civil war

AfD supporters and counter-protesters clash with police in the centre of Freiburg, Germany, as the mayor calls for 'peace'

As hundreds of people took to the city's streets to protest against the migrants, Freiburg's Mayor Martin Horn urged the AfD-organised protesters to remain 'peaceful' and refrain from 'further violence.'

The front of the 500-strong AfD protest holding a sign which says, 'Protect borders - save lives,' last night in Freiburg

'I hope the demonstrations will be peaceful and will not lead to further violence and hatred,' he told DPA news agency. 'In Freiburg, there is no room for criminals and such terrible crimes.'

Around 1,500 counter-protesters turned out to demonstrate against the AfD whom they accuse of exploiting the tragedy, according to DW.

German politicians have been facing tough questions about migrants' attitudes towards women and sexual violence since mass sexual assaults in Cologne during the New Year celebration some three years ago.