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.

Some in the country are drawing a link between the alleged ethnic identity of the attackers—“Arab or North African”—and the more than 1 million migrants and refugees, many of them from the Middle East and North Africa, who entered the country in 2015.

Groups that oppose migration into Germany said the incidents in Cologne showcased the dangers of accepting large numbers of migrants. Lutz Bachmann, who heads the anti-immigrant Pegida movement, blamed the German leadership for the alleged assaults.

German officials said justice would be color-blind, adding it was important not to tie the alleged assaults to the refugees and migrants.

Reker, Cologne’s new mayor, who was stabbed in October during a campaign event because of her pro-migrants view, said making such a connection was “completely improper.” And, she said, the city would prepare better for its upcoming Carnival season.

“We will explain our Carnival much better to people who come from other cultures, so there won’t be any confusion about what constitutes celebratory behavior in Cologne, which has nothing to do with a sexual frankness,” she said, according to comments reported by The New York Times.

German Chancellor Angela Merkel, who has become the face of Germany’s open-doors policy for refugees, called Reker on Tuesday to express her “outrage.” She said the perpetrators must be punished “regardless of their origin or background.”

And at a news conference on Tuesday, Heiko Maas, Germany’s justice minister, said the ethnic background of the alleged perpetrators was irrelevant.

“The law does not discriminate regarding a person’s origin or passport,” he said, according to the BBC. “All are equal before the law.”

Arnold Plickert, who heads the main police union in North Rhine-Westphalia, the region where Cologne is located, called the alleged assaults “a massive attack on basic rights,” adding there would be justice even if it has “politically uncomfortable” consequences.

He said, according to Deutsche Welle, “Any refugees who have a problem integrating into our open society and respecting the rights of other people” must be dealt with using the “full force of the law.” But he added that the public shouldn’t forget “the great majority of the people who have come to us have done so because their lives are no longer safe in their homelands.”