Police raided nine homes and businesses connected to Salafists in the city of Bremen at 6 a.m. (0400 UTC) on Tuesday.

A statement said special forces from Berlin and Hamburg, as well as the states of Mecklenburg-Western Pomerania and Schleswig-Holstein were also involved in the operation. The searches focused on four districts in the city's northwest - Gröpelingen, Lesum and Walle und Woltmershausen.

It's not clear whether any arrests were made. The Bremen prosecutor was expected to provide more information later Tuesday.

Authorities across Europe have been on high alert since the attacks in Paris and Brussels. Police in Germany have increasingly sought to crack down on Islamist extremists, particularly on sources of terrorism financing and support.

Salafism is typically used as an umbrella term for extremist interpretations of Sunni Islam. The number of Salafists in Germany has been steadily growing over the past few years, with recent estimates just under 8,000. But only a few hundred are considered to be potentially violent or willing to travel to fight in Syria and Iraq.

The head of Germany's domestic intelligence agency earlier this month said there were around 1,100 Islamists currently in the country that were considered to be highly dangerous.