A 32-year-old Iranian man has been arrested in Germany on suspicion of planning a chemical attack "motivated by Islamist extremism", officials said on Sunday.
Police and prosecutors said the man and his brother were detained overnight in the town of Castrop-Rauxel, north-west of Dortmund.
Security forces intervened after a "serious tip-off", said Herbert Reul, interior minister of Germany's most populous state, North Rhine-Westphalia.
"The suspect is suspected of having prepared a serious act of violence endangering the state by allegedly procuring cyanide and ricin," said a joint statement from Duesseldorf's public prosecutors' office and police.
Tabloid newspaper Bild reported that the tip-off about the alleged plot came from an allied intelligence agency.
It was not immediately clear how far advanced the plans were and whether the suspect had picked a specific target, but police confirmed it was suspected to be an attack motivated by Islamist extremism.
The suspect is believed to have supported a Sunni extremist group, German agency DPA cited an unnamed security official as saying.
Sunnis are a religious minority in Iran.
Even small amounts of ricin, which is produced from the seeds of castor oil plants, can kill an adult.
It can cause death within 36 to 72 hours of exposure to an amount as small as a pinhead. No known antidote exists.
ISIS-linked militants have carried out several terrorist attacks in Germany in recent years.
In 2016, 12 people were killed in a ramming attack at a Berlin Christmas market.
In 2018, German police arrested a Tunisian man and his wife on suspicion of planning to carry out a ricin attack in the name of ISIS. They were later found guilty and sentenced to 10 and eight years’ imprisonment, respectively.
They had procured enough ricin to potentially kill up to 13,500 people, a Duesseldorf judge said.
