Police in the German city of Bremen are warning of a potential danger from Islamic extremists there and say they are stepping up security measures.

A police statement said that officials received tips about activities of potentially dangerous Islamic extremists from a German federal authority on Friday evening. Saturday's statement said that police in the northwestern city are responding "with coordinated and adapted security measures."

Police gave no further details of the nature of the potential threat.

The warning comes amid heightened concern in Europe about terrorism following attacks this year in Paris and Copenhagen.

In mid-February, police in the northern German city of Braunschweig canceled a Carnival street parade over fears of a terrorist attack.