Women shout slogans and hold a sign that reads "Against Sexism, Against Racism" as they march through Cologne’s main railway station on Tuesday.

Outrage is growing in Germany over the reported sexual harassment of and assaults on women in the city of Cologne on New Year’s Eve that police have blamed on as many as 1,000 men of “Arab or North African” background.

The attacks—and robberies—allegedly occurred in Cologne’s historic square, which lies between the city’s main train station and its cathedral. News reports say 90 criminal complaints, including one of rape, were made at the city’s police department. Deutsche Welle, the German broadcaster, has spoken with some of the women who say they were assaulted.

Wolfgang Albers, the police chief, told DPA, the German news agency, the incidents were “an intolerable situation” for the city of 1 million, which is one of Germany’s most diverse. And Henriette Reker, Cologne’s mayor, said: “We cannot tolerate this development of lawlessness.”

Reker, city officials, and police met Tuesday to discuss the incidents. Deutsche Welle adds:

The police is currently analyzing footage from surveillance cameras as well as from photos and videos victims and witnesses took on their smart phones. But the police say it was impossible to catch perpetrators at the scene since the square was too crowded for victims to recognize the men. For months, Cologne police has had an eye on groups of young North African pickpockets operating in Cologne in groups of threes or fours. A big organized group like the one on New Year's Eve, however, is something "totally new," police investigators said.

It’s unclear why the incidents came to light only this week. Similar incidents were reported on New Year’s Eve in Hamburg and Stuttgart, German media reported, though on a smaller scale.