Cologne attacks: Police chief removed
The interior minister of North Rhine-Westphalia will announce on Friday that Wolfgang Albers is taking early retirement, reports say.
The police's handling of the night's events has been sharply criticised.
The violence outside the train station has sparked a debate on migration.
Also READ: Germany divided over expulsion of convicted asylum seekers
Gangs of men described as of North African and Arab appearance were reported to be behind the attacks.
German authorities say they have identified 18 asylum-seekers among 31 suspects linked to crimes committed in Cologne on New Year's Eve.
'I'll kill you'
"Of the 31 suspects whose names are known, 18 have asylum seeker status," interior ministry spokesman Tobias Plate told reporters on Friday, citing federal police figures.
The suspects include nine Algerians, eight Moroccans, four Syrians, five Iranians, two Germans and one each from Iraq, Serbia and the US, he said.
The state police in Cologne have recorded 170 complaints of crimes, 117 of which involve sexual assault. There were two allegations of rape.
Officers arrested two men, aged 16 and 23 and apparently of North African origin, overnight on Thursday in connection with the sex attacks, according to German media.
Officers also discovered a note on one of the men containing Arabic-German translations for phrases including "nice breasts", "I'll kill you" and "I want to have sex with you", the broadcaster said.
Cologne police say they are currently investigating 21 people in connection with the sexual assaults. It is not known how many of these are asylum seekers.
German Chancellor Angela Merkel has condemned the violence, saying Germany should examine whether enough was being done to ensure foreigners convicted of crimes in the country are deported.
She said "clear signals" had to be sent to those not prepared to abide by German law.
In a separate case, police have arrested four Syrians, aged between 14 and 21, over the suspected gang rape of two teenage girls in the southern German town of Weil am Rhein on New Year's Eve, according to German media.
The attack is not believed to be connected to the events in Cologne, the police statement said.
The identification of the attackers in Cologne 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.
Similar attacks to those seen in Cologne were also reported in Hamburg and in Stuttgart.
Police in several other European countries have also received complaints:
In Finland, police said they received reports of "widespread sexual harassment" in Helsinki on New Year's Eve, which they described as "a completely new phenomenon"
Police in the Swedish city of Kalmar have arrested two men over complaints by at least 15 women of sexual molestation
Austrian Interior Minister Johanna Mikl-Leitner pledged that police would take a "no tolerance" approach towards sexual assault after complaints of attacks in the city of Salzburg
Police in the Swiss city of Zurich said about six women had reported being robbed and sexually assaulted on New Year's Eve in attacks "a little bit similar" to those in Germany
"I feel so ashamed" - Anger on Arab-language social media
Facebook user Israa Ragab: "Every time I watch the TV and hear them saying the suspects could be from North Africa or Arabs I feel so ashamed and disgusted"
Deutsche Welle Arabic journalist Nahla Elhenawy: "The ugliness of our region is reaching Germany"