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 have 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.

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 chat rooms is at least as awful as the acts of those assaulting the women," he said. "This is poisoning the climate of our society."

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.

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."

Earlier, German Interior Minister Thomas de Maiziere strongly criticised police handling of the events in Cologne.

A crowd of about 1,000 men had gathered in the square outside the main railway station on New Year's Eve, letting off fireworks. Many were drunk and aggressive.

Police eventually evacuated the area because of the risk of injury from the 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.

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".

On Wednesday, Cologne police said the number of criminal complaints received had risen to 106. At least three-quarters of those were of sexual assault, including two alleged rapes.