The mayor of Cologne has been criticised for suggesting a "behaviour guide" for women hoping to protect themselves in the wake of a series of sexual assaults committed by a group of 1,000 men at the city's main train station on New Year's Eve. Mayor Henriette Reker suggested women should keep "an arm's length away" from men and to not stray from their own group when out at night in order to protect themselves from harassment following the mass assaults outside Cologne Cathedral by men described as from the "north African or Arab world".

Following a crisis management meeting with police chiefs, Reker − who herself was recently the victim of an attack after being stabbed in the neck apparently over her work with refugees − outlined a "code of conduct" illustrating how women should act, such as asking bystanders for help and to inform the authorities of an assault.

She said: "There's always the possibility of keeping a certain distance of more than an arm's length – that is to say to make sure yourself you don't look to be too close to people who are not known to you, and to whom you don't have a trusting relationship."

Many people have condemned the comments by the mayor as either blaming the women for being attacked or mocking the suggestions they could have easily protected themselves. On Twitter, many users wrote about their frustrations using the hashtag #armlaenge [arm's length] reported The Local.

Anne Roth wrote: "The most annoying thing is that we didn't know this one-arm's-length thing before. Think what women could have prevented!". Twitter user @Tulpenbieger added: "Neo already knew that in the Matrix, you can hold off a whole lot of things by keeping an arm's length distance".

Reker also called for a "better explanation" as to what constitutes acceptable behaviour at public gatherings to the migrant community ahead of the Cologne Carnival in February.

"We need to prevent confusion about what constitutes happy behaviour and what is utterly separate from openness, especially in sexual behaviour." Police have downplayed suggestions the perpetrators were immigrants who had recently arrived in Germany and had been known to police for some time.

Heiko Maas, Germany's justice minister, also condemned the attacks and called for better police protection when similar attacks occurred in Hamburg. He tweeted: "The despicable attacks on women will not be tolerated. This is obviously a completely new dimension of organised crime."