German authorities need to quickly determine whether a string of New Year's Eve sexual assaults and robberies in Cologne blamed largely on foreigners may be linked to similar offences in other cities, the justice minister said in comments published Sunday.

Authorities and witnesses say the attackers were among about 1,000 people, mostly men, gathered at Cologne's central train station, some of whom broke off into small groups that groped and robbed women.

"If such a horde gathers in order to commit crimes, that appears in some form to be planned," Justice Minister Heiko Maas told the newspaper Bild. "Nobody can tell me that this was not co-ordinated or prepared."

The attacks are still being investigated, but police have said their focus is on suspects of primarily North African origin, which has put pressure on Chancellor Angela Merkel's government and its open-door policy to asylum seekers. Nearly 1.1 million refugees and migrants arrived in Germany in 2015 alone.

She announced a proposal Saturday that would make it easier to deport refugees and migrants who commit crimes, which still needs parliamentary approval.

Cologne police said Sunday that 516 criminal complaints had now been filed with them in connection to the New Year's Eve attacks, about 40 per cent of which involve allegations of sexual offences.

They also announced that on Saturday night they arrested a 19-year-old Moroccan man on allegations he stole a 23-year-old woman's cellphone on New Year's Eve, and had identified 19 other suspects by name. Police said the Moroccan, who they said has been involved in various crimes since 2013, isn't accused of a sexual offence, but the investigation is ongoing.

Paris knife attacker linked to Germany 

In a separate development that seemed likely to provide more grist for opponents of Merkel's policies, police in the western state of North Rhine-Westphalia on Saturday raided an apartment at a shelter for asylum seekers in Recklinghausen that they said had been occupied by an extremist who French police fatally shot on Thursday as he ran up to a Paris police station wielding a butcher's knife and wearing a fake explosives vest.

French Interior Minister Bernard Cazeneuve said in remarks Sunday that the man was also believed to have lived in Luxembourg and Switzerland.

Germany Paris Attacks

The mug shot provided Sunday, Jan. 10, 2016 by the police in Duesseldorf, western Germany, shows a man that applied for asylum in Germany with name Walid Salihi. The man was fatally shot by French police on Thursday as he ran up to a Paris police station wielding a butcher's knife and wearing a fake explosives vest. He had first entered Germany in 2013 after living for five years illegally in France, and had gone by at least seven names, identifying himself as a Tunisian, Moroccan and Georgian. (Landeskriminalamt Recklinghausen via Associated Press)

North Rhine-Westphalia state police chief Uwe Jacob described the suspect as a smalltime criminal known to authorities by several aliases, who had a record that included weapons charges, drug trafficking and causing bodily harm and had spent at least a month in jail.

He said there are no indications the man was part of an extremist network, but that a self-drawn Islamic State flag was found in his room, the dpa news agency reported.

At a news conference in Duesseldorf, Jacob told reporters that the man had first entered Germany in 2013 after living for five years illegally in France, and had gone by at least seven names, identifying himself as a Tunisian, Moroccan and Georgian. He lived in several German cities and moved to Recklinghausen at the beginning of last August.

Suspects called 'modern-day nomads'

Separately, police in Hamburg are also investigating sexual assaults and thefts in the St. Pauli district similar to those in Cologne, which occurred on a smaller scale in the northern city on New Year's Eve. Authorities in Sweden and Finland are also investigating similar incidents in their countries.

"All connections must be carefully checked," Maas said. "There is a suspicion that a particular date was chosen with expected crowds. That would then be a new dimension."

Of an initial 31 suspects detained by police for questioning, 18 were asylum seekers but there were also two Germans, an American and others, and none of them were accused specifically of committing sexual assaults.

GERMANY-ASSAULTS/

Women shout slogans and hold up a placard that reads 'Against Sexism - Against Racism' as they march through the main railways station of Cologne on Jan. 5. About 90 women have reported being robbed, threatened or sexually molested at the New Year's celebrations outside Cologne's cathedral by young men. (Wolfgang Rattay/Reuters )

Police have released few details, but Bild on Sunday said one, a 22-year-old Tunisian, was registered at a refugee centre in a neighbouring state, while two Moroccans aged 18 and 23, were apparently in the country illegally, according to their attorney.

"Our clients are modern nomads," attorney Ingo Lindemann told the newspaper. "They're not war refugees, but more like grown street children who move with the flow of refugees across Europe."

Cologne police wouldn't confirm the report on the three and Lindemann didn't immediately return a phone call or an email.

Germany Cologne Crimes

Participants of a women's flash mob demonstrate against racism and sexism in Cologne, Germany, Saturday, January 9, 2016. (Juergen Schwarz/Associated Press)