Ralf Jäger, the interior minister of North Rhine-Westphalia state, released initial findings of a criminal probe over the crime spree that has piled pressure on Chancellor Angela Merkel over her liberal stance towards refugees.
"Witness accounts and the report by the (local) police as well as findings by the federal police indicate that nearly all the people who committed these crimes were of foreign origin," he said.
Although no formal charges have been laid, Jäger said the attackers emerged from a group of more than 1,000 "Arab and North African" men who gathered between the main railway station and the city's iconic Gothic cathedral during the year-end festivities.
But Jäger also reserved some criticism for the police, following up on his decision to suspend Cologne police chief Wolfgang Albers on Friday.
Commanders had not called on "desperately needed reinforcements for the unexpected developments in the situation" at the main railway station, he told fellow representatives in the Düsseldorf state parliament at a special session on Monday.
Jäger, Cologne mayor Henriette Reker, and others have also accused the police of hiding the racial background of the attackers in the days after January 1st.
"The picture the police gave out on New Year's Eve is unacceptable," he said.
Racist violence breaks out in Cologne
Amid concerns over reprisal assaults, police said a mob attacked a group of six Pakistanis late Sunday in Cologne, two of whom had to be hospitalised.
Shortly afterwards, five unidentified assailants attacked a 39-year-old Syrian national, injuring him slightly.
After far-right protests erupted in Cologne during the weekend, a sister group of the xenophobic PEGIDA movement was due to hold another rally later Monday in the eastern city of Leipzig.
A police water cannon truck is seen in the background behind Pegida demonstrators in Cologne on Sunday. Photo: DPA
In the face of outrage over the New Year's Eve violence, Merkel has taken a tough line against convicted refugees.
She has signalled her backing for changes to the law to ease expulsion rules, with officials within her ruling coalition expected to swiftly negotiate the proposals this week.
Police said late Sunday that more than a week on from New Year's Eve, some 516 complaints had now been lodged, including 40 percent that are related to sexual assault.
Witnesses described terrifying scenes of hundreds of women running a gauntlet of groping hands, lewd insults and robberies in the mob violence.
'Assaults were planned'
The scale of the Cologne assaults has shocked Germany and put a spotlight on the 1.1 million asylum seekers who arrived in the country last year.
It has also fuelled fear, with a poll published by the Bild am Sonntag newspaper saying that 39 percent of those surveyed felt police did not provide sufficient protection for the public at large, while 57 percent did.
And just under half (49 percent) believed the same sort of mob violence could hit their hometown, reported the newspaper which headlined its article with the question: "Is the New Year's Eve scandal the result of wrong policies?"
A separate poll by broadcaster RTL found that 57 percent of Germans feared crime would rise along with the record influx of asylum seekers, while 40 percent disagreed.
Nevertheless a majority - 60 percent - said their opinion of foreigners has not changed, while 37 percent said they have become more critical and negative about newcomers.
Justice Minister Heiko Maas. Photo: DPA
Justice Minister Heiko Maas has said he believed the violence in the western city of Cologne was organised.
"For such a horde of people to meet and commit such crimes, it has to have been planned somehow," he told Bild am Sonntag newspaper.
"No one can tell me that this was not coordinated or planned. The suspicion is that a specific date and an expected crowd was picked," he said.
Quoting confidential police reports, Bild am Sonntag said some North Africans had sent out calls using social networks for people to gather in Cologne on New Year's Eve.
Separately in Hamburg, police said they had received 133 criminal complaints for similar violence during the northern city's own New Year's Eve celebrations.
With thousands of asylum seekers still streaming into Germany every day, Merkel has come under fire, even within her own conservative alliance, who want her to put a cap on the number of refugees in the country.
Critics have questioned Germany's ability to integrate the unprecedented number of newcomers, many of whom hail from Syria, Iraq and Afghanistan.
Merkel had until now not wavered from her stance but has adopted a firmer tone after Cologne, even pledging to change the law to make it easier to expel convicted asylum seekers.
"It's not premature to speak of a turning point (after Cologne), or at least the reinforcing of a trend that had already started to take shape lately," Andreas Rödder, contemporary history professor at Mainz University told AFP.