German state interior minister Ralf Jaeger has said migrants were almost exclusively responsible for the attacks on women in Cologne on New Year's Eve.
More than 100 women reported being threatened, robbed or molested during the city's celebrations.
The minister's comments come amid reports a group of Pakistanis and a Syrian were violently attacked by about 20 unknown assailants on Sunday in the city.
A protester took to the streets of Cologne naked after a series of violent and sexual attacks against women on New Year's Eve.
Swiss artist Milo Moire braved the cold to bare all in the German city's cathedral square, holding up a sign which read: "Respect us! We are not fair game even when naked".
She said her protest was a reaction to some advice from officials warning women to keep men at arm's length, saying: "It is a matter of course we have worked for in the past 50 years, that I can live as a woman the way I want to, in freedom."
Police were on patrol in the square but did not interfere with the performance - though they did usher away a number of young men in the area around the main station and cathedral.
Witnesses have described the hundreds of men who carried out the attacks as being of "Arab or North African origin," but little concrete evidence has been released to date on who was responsible for the assaults.
The German Chancellor wants increased powers to block foreigners from being granted asylum if they have any sort of criminal record.
Around 400 people gathered in Cologne to demonstrate against violence against women following a wave of assaults on New Year's Eve.
Authorities in Cologne are holding crisis talks on Tuesday after a string of sexual assaults by large gangs of men.