A series of New Year’s Eve attacks attributed to Arab and North African men threatens to fan the flames of Germany’s refugee debate.

The wave of violence overnight on Thursday resulted in dozens of reports of sexual assault and robberies around the city’s main train station, where a crowd of roughly 1,000 men had congregated, police said, according to Spiegel online.

“We will not tolerate such cowardly and abhorrent attacks,” German Justice Minister Heiko Maas said Tuesday. “This is apparently an entirely new dimension of organized crime.”

More than 90 criminal complaints were filed, and about a quarter of them cited sexual harassment or groping, with most others citing theft, Cologne Police Chief Wolfgang Albers said. Small groups of men would emerge from the larger crowd to surround, harass and sometimes steal from women, the police chief said.

The crimes were committed by a group of men “who from appearance were largely from the North African or Arab world,” Albers said. Similar attacks were reported in Hamburg and Stuttgart, according to the BBC.

Cologne Mayor Henriette Reker described the attacks as “outrageous” and called an emergency meeting.

“We cannot tolerate a legal vacuum here,” said Reker, who was elected last October while hospitalized after an opponent of her pro-refugee policies stabbed her in the neck.

Germany has been inundated in recent months by refugees of the Syrian conflict.