Thirty-one suspects, including 18 asylum seekers, are under investigation over offences including assault and theft in Cologne on New Year's Eve, Germany's interior ministry said Friday.

"Of the 31 suspects whose names are known, 18 have asylum seeker status," said ministry spokesman Tobias Plate, adding that their alleged offences were "mostly theft and causing bodily harm". 

"Three complaints have also been filed for sexual offences, but the perpetrators for these have not been identified," he added.