BERLIN — German authorities said on Tuesday that coordinated attacks in which young women were sexually harassed and robbed by hundreds of young men on New Year’s Eve in the western city of Cologne were unprecedented in scale and nature.
The assault, which went largely unreported for days, set off a national outcry after the Cologne police described the attackers as young men “who appeared to have a North African or Arabic” background, based on testimony from victims and witnesses. More than 90 people have filed legal complaints, the police said on Tuesday.
The police in Hamburg also said that 10 women had reported being sexually assaulted and robbed in a similar fashion on the same night, and they urged witnesses to come forward.
Germany took in more than one million migrants last year, and with the country struggling to deal with the political, social and wider consequences of the influx, the delayed public response has led to concerns that the authorities were playing down the seriousness of the assault to prevent it from becoming a point of contention in the broader debate.
The assault took place late on Thursday on the vast public square in front of the city’s main train station, a central transit point for anyone coming or going from a fireworks display over the Rhine and the bars and nightclubs in the heart of the city, in the shadow of its landmark cathedral.
Heiko Maas, Germany’s justice minister, warned on Tuesday against linking the assaults to the influx of refugees, saying that the ethnicity of the perpetrators was irrelevant.
“The rule of the law does not look at where someone comes from but what they did,” Mr. Maas told reporters in Berlin. “We will investigate what circles the perpetrators may have come from.”
The Cologne police say they believe several hundred men, ages 15 to 35, were involved in the violence that began in the early hours of the New Year, after the square was cleared because men had been throwing firecrackers into the crowd.
Wolfgang Albers, Cologne’s chief of police, said the assaults had taken place in the chaos that followed, as the square was emptied. The men appeared to have broken into smaller groups, the police said, with each one encircling a woman; while some would grope the victim, others would steal her wallet or cellphone.
One victim reported that she had been raped, the police said.
Henriette Reker, Cologne’s mayor, called a crisis meeting on Tuesday to address the issue. Ms. Reker, who was stabbed during a campaign event in October by an attacker who opposed her welcoming attitude toward migrants, called the assault “absolutely intolerable” and pledged her support for the authorities’ investigation.
The city holds a large festival every year before Easter, when thousands of costumed revelers throng the streets to celebrate with parades and parties, and Ms. Reker echoed the concerns of many about safety during the Carnival season.
In an effort to prevent further violence, Ms. Reker said that city officials would begin working on measures to help young women protect themselves and to explain the city’s attitudes and norms to its many newcomers.
“We will explain our Carnival much better to people who come from other cultures,” she said, “so there won’t be any confusion about what constitutes celebratory behavior in Cologne, which has nothing to do with a sexual frankness.”
Cologne, with roughly one million inhabitants, is among Germany’s most ethnically diverse cities, and it took in more than 10,000 refugees last year, many of them young men from Afghanistan, Iraq and Syria. The city authorities said they would increase security after the assaults, as they continued to search for suspects.
The euphoria that accompanied the first wave of arrivals in Germany this summer has since given way to growing unease about the difficulty of integrating hundreds of thousands of people of a different religion and who were raised in a different culture.
Far-right and anti-immigrant groups in Germany, and others who oppose the influx, swiftly seized on the episode, saying it demonstrated the dangers associated with accepting huge numbers of migrants.
Lutz Bachmann, head of the anti-immigrant Pegida movement, accused German leaders on Twitter of complicity in the assault. In a post that named Ms. Merkel; her deputy, Sigmar Gabriel; and other politicians, Mr. Bachmann said, “You are all responsible for the abuse in Cologne!”
