The 26-year-old migrant who killed one person and injured six others in a knife attack in a Hamburg supermarket on Friday was known to German security forces as an Islamist, the city-state's interior minister says.

Gambian refugee Bakery Jatta has signed a contract with German Bundesliga side Hamburg, the club said Tuesday, in what local media dubbed a "football fairytale".

The head of Cologne's police force is leaving his post "to restore public trust in the police" following scores of attacks on women in the city on New Year's Eve, German media report.

Residents of the German city of Hamburg have voted against hosting the 2024 Olympic and Paralympic Games.

Tens of thousands of people have taken part in a "day of action" in several European cities - and in Australia - in support of refugees and migrants.

Facebook has been prevented from stopping users in Germany creating accounts under false names.