Germany's top security official is stressing that anyone involved in New Year's Eve assaults and robberies in Cologne on must be punished regardless of where they come from, and says that if refugees were involved it must be addressed openly.

Events in Cologne, involving a crowd of a thousand men described as being of Arab or North African origin, have shaken Germany and added fuel to debate about its ability to integrate large numbers of migrants.

Police say at least 90 criminal complaints were filed. They say some men in the crowd formed smaller groups and surrounded women.

Interior Minister Thomas de Maiziere told Wednesday's edition of the Bild daily: "All of the perpetrators, of whatever origin, must be punished. If refugees were among them, we must address that openly."