Berlin police said Wednesday they have arrested a German man suspected of being connected to extremists and seized a cache of weapons and ammunition during raids but found no evidence of an imminent attack.
The suspect, an unnamed 40-year-old, will come before a judge, the police and the public prosecutor said in a joint statement.
The Tuesday evening sweep of four sites in the German capital allowed police to "seize arms, weapon parts and large quantities of ammunition," according to the statement, which did not give details about the type of guns found.
"Due to concerns they could be used for attacks, Berlin prosecutors took over the investigation," the authorities said.
"After it was determined that (the suspect) displayed an increased willingness to use violence, it was decided to arrest him. The suspicion of weapon possession was confirmed, without any evidence so far of a concrete attack plan."
The suspect came to their attention in the course of another criminal probe that started in June with the arrest of a drug dealer, they added.
German police have been on high alert to the threat of attacks, particularly after a truck rampage claimed by ISIS killed 12 people at a Christmas market in Berlin last December.
A report published last month found that Berlin authorities had missed several opportunities to arrest and deport the driver, Tunisian asylum seeker Anis Amri.
Officials admitted a series of security failures that allowed Amri to register under multiple identities and evade authorities while he was in contact with militants.
Germany's domestic intelligence agency has warned of further attacks by radicalized people given growing numbers of foreign militants returning from war zones in Syria and Iraq.