The city of Cologne in Germany has called for crisis talks after 1,000 "drunk and aggressive young men" that were reportedly of Arab or North African appearance sexually assaulted at least 80 women on New Year's Eve.
Cologne police chief Wolfgang Albers called it "a completely new dimension of crime," according to BBC News, and said that most of the crimes were robberies, but women were also groped and raped.
Mayor Henriette Reker added that the attacks were "monstrous," and said that authorities will take a tough stand against such crime.
"We cannot allow this to become a lawless area," she said.
The Telegraph reported that incidents of violence were reported in Hamburg as well, with witnesses describing groups of five to 15 men "hunting" down women on the streets.
German Justice Minister Heiko Maas stated that "we won't tolerate these abhorrent assaults on women – all those responsible must be brought to justice," but also warned that it would be incorrect to talk about the crimes only in terms of the ongoing refugee crisis in Europe.
BBC's Damien McGuinness in Berlin said that the attacks have "shocked" Germany, especially given that they appear to have been planned.
"What is particularly disturbing is that the attacks appear to have been organized. Around 1,000 young men arrived in large groups, seemingly with the specific intention of carrying out attacks on women," he wrote.
Germany has welcomed close to 800,000 refugees coming in from Syria and other places in the Middle East fleeing war and terrorism, though the influx of refugees has caused significant tension and debate among European nations.
Chancellor Angela Merkel's open-door policy on immigration has also been blasted by the anti-immigrant PEGIA movement, which has staged marches in several cities, warning that Germans will find themselves in danger.
"I am convinced that Mrs. Merkel's politics are against national interests," PEGIDA supporter Max Haupt said during a rally in Dresden back in October. "I'm very disturbed about that. It's almost treason. She has forgotten the oath she gave when she was sworn in."
Merkel has defended her policy, however, arguing that there is no practical way to limit the number of incoming refugees.
"You cannot just close the borders," the German leader said in an interview.
Merkel has met some opposition within her Christian Democratic Union party, however, as MP Steffen Bilger tweeted after the NYE assaults:
"It can't go on like this. Urgently needed: reduction of influx, secure borders, intensifying of deportations and meaningful justice. #Cologne."
German authorities also had to deal with a high level bomb threat in Munich on NYE, with intelligence sources warning that up to seven suicide bombers had planned to attack two of the city's train stations.
The Guardian noted that the threat forced police to close down sections of the city, deploying about 550 officers to several locations.
Munich police spokeswoman Elizabeth Matzinger said that there is strong reason to believe the Islamic State terror group was behind the planned attacks.
"Investigations are happening, but I cannot give out any details, that is a tactical information," Matzinger said. "I can't confirm whether they are Iraqis, but it was apparently a group of five to seven people affiliated to IS [ISIS]."