Police in Germany will have to rethink their tactics following attacks on women in the city of Cologne on New Year's Eve, a senior official has said.
Ralf Jaeger, interior minister for North Rhine-Westphalia, said police had to "adjust" to the fact that groups of men had attacked women en masse.
Three suspects had been identified, he said, but no arrests had been made.
Scores of women say they were robbed or sexually assaulted by men, reportedly of Arab or North African appearance.
Mr Jaeger also warned that anti-immigrant groups were trying to use the attacks to stir up hatred against refugees.
"What happens on the right-wing platforms and in chatrooms is at least as awful as the acts of those assaulting the women," he said. "This is poisoning the climate of our society."
What we know of the NYE attacks
- Scores of women say they were sexually assaulted and had mobile phones and bags stolen by large groups of men during New Year celebrations in the centre of Cologne
- As many as 1,000 men - described as drunk and aggressive and many of North African and Arab appearance - were reported to have been behind the attacks
- Cologne police say they have received 121 criminal complaints - at least three-quarters of those were of sexual assault, including two alleged rapes
- Sixteen suspects have been identified but no-one has yet been arrested, police say
- Similar attacks were reported in Hamburg, where 30 complaints were filed, and in Stuttgart
Mr Jaeger said police had to ensure there was no repeat of the events of New Year's Eve.
"Something like this must not happen again - not only in Cologne, but also in other big cities," he said.
"The police have to conceptually adjust to the fact that there are apparently groups of perpetrators, who assault women en masse. This must not happen in our society and the police as well as the city authorities have to react to it."
Correspondents say the identification of the attackers as North African or Arab in appearance has caused alarm in Germany because of the influx of more than a million migrants and refugees in the past year. Many of the incomers have fled the conflict in Syria.
The "anti-Islamisation" Pegida movement and the right-wing AfD have said the attacks were a consequence of large-scale migration.
But Cologne's mayor said there was no reason to believe those behind the attacks were refugees.
At the scene: UK teenager tells of Cologne violence
We heard a woman screaming and crying somewhere in the midst of the crowd, appearing to be escaping from a foreign man, who was shouting back and pointing his finger at her and chasing her with his accomplices.
Later on, we saw two men corner women at the cathedral and touch them while they were screaming for help and trying to fight back.
Earlier, German Interior Minister Thomas de Maiziere strongly criticised police handling of the events in Cologne.
Police had evacuated the area around the main railway station where some 1,000 men, many of whom were described as drunk and aggressive, had been letting off fireworks.
But gangs of youths soon returned and carried out dozens of attacks over a number of hours with little apparent response from the local authorities until well after midnight.
Mr de Maiziere criticised police for allowing the attackers to return. The square was evacuated, he said, "and then later these events take place and they wait for complaints. The police shouldn't work like this".
Cologne police chief Wolfgang Albers has rejected criticism of his officers, describing what happened as "a completely new dimension of crime".
But police union chief Rainer Wendt said a lack of resources had meant that the Cologne force had been unable to clear the square properly.
In the city of Hamburg, more than 30 complaints have been filed by women saying they were indecently assaulted or robbed on Hamburg's Reeperbahn on New Year's Eve and police in Stuttgart say several women were attacked at Schlossplatz in the city centre.
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