Syrians, Pakistanis and African men were among the victims of Sunday's mob violence in the western city on Sunday, the scene of a series of New Year's Eve sexual assaults on women that have been blamed on migrants.
There were four separate attacks which police were referring to as "anti-foreigner crimes," crime division chief Norbert Wagner said.
Since Thursday, several people known for involvement in hooliganism had issued calls on social media for people to join several "non-violent strolls" in central Cologne, he said.
Such a term is a common euphemism for a march among far-right groups.
"In these four assault cases, we have to presume they were connected with these so-called strolls," said Wagner, adding that far-right activists were among the marchers.
Express newspaper reports that a group of hooligans and bikers had arranged on Facebook to go on a “manhunt” in the Cologne city centre and “clear the place out”
So far, none of the perpetrators have been caught although police questioned 153 people on Sunday night, 13 of whom were known for previous far-right offences.
Another 18 had ties to the city's biker gangs or were employed as club doormen, police said.
In the first attack, which took place in the early evening, some 25 men chased a man of African appearance who ran to seek protection from a group of six Pakistanis.
"The pursuers then beat and kicked these young Pakistani men," Wagner said.
In another attack, eight people beat a 39-year-old Syrian at the central railway station. Two other assaults targeted three men from Guinea, and another Syrian man.
Police detained four people, but none of them led to a formal arrest, with the investigation and the investigation was ongoing.
Operations chief Michael Temme said Cologne police would step up city patrols for the foreseeable future, especially around the central railway station area near the landmark Cologne Cathedral.
"We will be highly active and will do everything possible" to prevent repeat attacks, he said.
Cologne police have come in for criticism for failing to prevent the New Year's Eve chaos, when hundreds of women were groped and robbed.