Baku, November 20 AZERTAC
The attack at the "No Name" bar took place around 2:45 local time (1:45GMT) in the Nippes district near the city center, according to the Koelner Stadt Anzeiger newspaper.
"The door opened and shots were fired in front of and possibly inside the bar," police spokesman Alexander Schwarzer said, as cited by the outlet.
Police detained two suspects. The bar has been closed for visitors since the nightly shooting.
Police have been on the alert across Europe following last Friday's terrorist attacks at several public venues across Paris, including at local restaurants and a bar. The gun and bomb attacks killed 129 people and injured over 300.