West German police arrested a man in the city of Duisburg after receiving information about a potential attack, the police said on Tuesday.
The man, 29, was a previously convicted Islamist militant and is suspected of planning an attack on a pro-Israeli demonstration, according to German newspaper Spiegel.
The apartment of the man in the Dellviertel neighborhood was searched and he was temporarily taken into custody, the police said in a statement.
The man had searched online for pro-Israeli events and jihadist content and it is unclear whether he already had a specific demonstration in mind for the potential attack, Spiegel reported.