A string of sex assaults and robberies during New Year’s celebrations in Germany has fuelled debate about the country’s ability to integrate large numbers of migrants, after police said that men who targeted dozens of women in the western city of Cologne appeared to be of “Arab or North African origin.”

在警方说了那些在科隆市西部攻击数十名妇女的男人似乎是“阿拉伯人血统或北非血统”后，发生在德国新年庆祝活动中的一连串的性攻击和抢劫事件点燃了关于德国的整合大量移民之能力的辩论。

Political leaders including Chancellor Angela Merkel condemned the attacks, though many also warned against hasty conclusions about the perpetrators. But to some Germans already uneasy about the one million asylum-seekers their country took in last year the incident seemed to confirm simmering fears.

“Is this the ‘cosmopolitan and colourful’ Germany that Merkel wished for?” asked Frauke Petry, leader of the nationalist party Alternative for Germany.

Ms. Petry’s party has called for a clampdown on the number of asylum-seekers allowed into the country, a sentiment shared among a growing number of supporters in Ms. Merkel’s own centre-right bloc.

“It’s unacceptable that women are sexually molested and robbed by young migrants on the streets and public squares of German cities at night,” said Andreas Scheuer, general-secretary of the Christian Social Union, the Bavarian wing of Ms. Merkel’s party.

“Whoever won’t accept our rules for living together, including respect for women, can have no place in our society here in Germany,” said Mr. Scheuer. His party has called for a cap of 200,000 asylum-seekers in Germany a year, a demand its lawmakers are likely to repeat at a meeting with Ms. Merkel on Wednesday.

Others in Germany cautioned against tying the refugee question to the issue of street crime when the full facts of the incident aren’t known yet.

“It’s completely improper … to link a group that appeared to come from North Africa with the refugees,” Cologne’s mayor Henriette Reker told reporters after a crisis meeting with police Tuesday. Syria, Albania and Kosovo were the top three countries of origin for asylum-seekers in Germany last year.

Cologne’s police chief Wolfgang Albers said no arrests have been made yet. “We don’t currently have any suspects, so we don’t know who the perpetrators were. All we know is that the police at the scene perceived that it was mostly young men aged 18 to 35 from the Arab or North African region.”

Mr. Albers urged witnesses to come forward, especially if they recorded videos of the attacks. At least 90 criminal complaints have been filed, including one allegation of rape, police said.

Police said the attackers had gathered in large numbers near the city’s main train station, drinking alcohol, releasing fireworks and mingling with other revellers.

Separately, police in the northern city of Hamburg appealed for witnesses who observed similar sexual assaults and thefts in the St. Pauli district on New Year’s night.

German Justice Minister Heiko Maas said the attacks shouldn’t be used to bolster an anti-refugee agenda. “In criminal law what’s important is proving a crime, and everyone is equal before the law,” Mr. Maas said. “It doesn’t matter where someone comes from, it matters what they did and that we can prove it.”

Ms. Merkel’s office said the chancellor had called Mayor Reker earlier in the day and “expressed her outrage about these despicable assaults and sexual attacks, that demand a hard response by the forces of law.”

She also called for everything to be done “to find the perpetrators as quickly and comprehensively as possible and to punish them without regard to their origin or background,” her office said.

German authorities have regularly dismissed the idea that the influx of refugees is leading to a disproportionate rise in crime. At the same time, security officials have warned that violence against asylum-seekers has increased steeply over the past year.