Flowers and posters are placed in the square between the city cathedral and the railway station in Cologne, Germany, Jan. 11, 2016, where the vast majority of dozens of New Year's Eve assaults on women took place. REUTERS/Wolfgang Rattay

Over the weekend, some 20 unidentified assailants cornered and attacked migrants in the German city of Cologne. The victims included a half dozen Pakistani men, two of whom were hospitalized. There was a separate assault on a Syrian asylum seeker, who was lightly injured after being set upon by five attackers.

The incidents follow a grim spate of attacks that took place in Cologne and a handful of other northern European cities on New Year's Eve. In Cologne, mobs of men, the majority of whom were reported to be of North African or Arab origin, robbed and sexually assaulted female passersby and clashed with an overwhelmed, startled police force.

Authorities in the western German city reported Monday that 516 criminal complaints have been filed in relation to the New Year's Eve events. Some 40 percent of the complaints involve allegations of sexual assault. German Justice Minister Heiko Maas said Sunday that the disturbances and mayhem, which unfolded after hundreds of men congregated by Cologne's main train station, were likely prearranged.

"If such a horde gathers in order to commit crimes, that appears in some form to be planned,'' he told the Bild, a leading German newspaper. "Nobody can tell me that this was not coordinated or prepared."

The scenes of chaos deepened a growing backlash to the open-door policy of German Chancellor Angela Merkel toward Syrian refugees. Germany admitted 1.1 million asylum seekers in 2015, even as nations elsewhere in Europe sought to shut the door on all arrivals.

Still, there is no clear link between the New Year's Eve assaults and refugees. German authorities, as my colleague Anthony Faiola reports, are struggling to tamp down hate speech against Muslims and migrants. Officials even won the cooperation of companies such as Facebook, Twitter and Google to curb offensive material and comments online.

"As abominable as the crimes in Cologne and other cities were, one thing remains clear: there is no justification for blanket agitation against foreigners," Maas said.  He suggested that race-baiting provocateurs "appear just to have been waiting for the events of Cologne."

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