German authorities said yesterday that nearly all the suspects in a rash of New Year's Eve violence against women in Cologne were "of foreign origin", as foreigners came under attack amid surging tensions.

Ralf Jaeger, 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, Jaeger 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.

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.

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.