
Police in the western German city of Essen said Tuesday they have arrested a man after receiving "indications of a possible attack scenario", AFP reported.
Whether the man who is "known to police" was preparing an attack "is under investigation", police said in a statement.
The man was arrested at his home in Duisburg, which was searched by the police, the statement added.
Several media reports said the man is a 29-year-old German-Egyptian national who plotted to attack a pro-Israel demonstration.
The Der Spiegel weekly and Bild newspaper reported that police had received information from a foreign intelligence service that the man had, among other things, searched the internet for pro-Israeli demonstrations and consulted jihadist content, fuelling fears that he wanted to plan an attack.
Der Spiegel, citing sources close to authorities, reported that it was unclear whether the suspect had been targeting a specific demonstration.
The alert was deemed sufficiently serious and the suspect, known as Tarik S. was arrested under the Risk Prevention Act, according to the media reports.
Tarik S. travelled to Syria via Turkey at the end of 2013, where he joined the Islamic State (ISIS) group, according to Der Spiegel.
On his return to Germany in 2016, he was arrested at Frankfurt airport and sentenced in 2017 to five years' imprisonment for membership of a terrorist group by a juvenile court, the report said.
Germany has been on high alert in recent years, following a series of terrorist attacks. The worst such attack took place in December of 2016, when Tunisian terrorist Anis Amri killed 12 people and injured dozens more when he drove a truck into a Christmas market in Berlin.
Tensions have risen in recent days as hundreds of pro-Israel and pro-Palestinian Arab demonstrations have been taking place in Germany since the Hamas massacre in Israel on October 7.
The country has seen a sharp rise in antisemitic incidents in the wake of the Israel-Hamas war. In one incident, a synagogue in the German capital of Berlin was firebombed by two assailants. The incident is being investigated as a hate crime.
Police have increased security for Jewish institutions across Germany in recent days.