Police in Cologne say they’ve detained hundreds of men “seemingly of African descent” as part of operations to prevent a repeat of the attacks seen in the German city a year ago.

Cologne police say the men were detained at two main train stations so that officers could question them and check their identities.

Authorities fielded over 1,500 officers across Cologne for New Year’s celebrations in response to criticism that they failed to stop hundreds of robberies and sexual assaults — blamed largely on men of North African origin — last year.

Some revelers this year complained on Twitter that police appeared to be detaining people based on their appearance alone.

By early Sunday police had received reports of two women being sexually assaulted in Cologne. One man was arrested