Anti-terrorist agents in Germany have detained a 32-year-old Iranian man who is accused of planning an Islamist-motivated attack using chemicals.

The DPA news agency reported Sunday that the man along with another one has been arrested in Castrop-Rauxel in Germany's north-western Ruhr area.

Police say he is suspected of having obtained the toxins cyanide and ricin which are highly toxic and listed as biological weapons by Germany.

"The accused is suspected of having prepared a serious act of violence that is dangerous to the state," investigators said.

"Evidence has been secured and is being evaluated," added DPA.

It has not yet been decided whether the 32-year-old will be brought before a court, but police said, it may carry a prison sentence of between six months to 10 years.

Tabloid newspaper Bild reported that German authorities had been watching the men for days, after receiving a warning from a "friendly intelligence agency."

According to local media, the raids were carried out by agents wearing protective suits, due to the chemical hazard.

Germany has been targeted in recent years by several Islamist attacks. In 2016 a truck attack on a Christmas market killed and injured dozens.

German domestic intelligence services say the number of supporters of Islamist causes has decreased by 1.5 percent in 2021, citing the "military breakup" of the ISIS group.