32-year-old said to have planned an Islamist attack in Germany

German investigators probing a planned attack using ricin and cyanide have not found any traces of the toxins.

They searched for it in the residential premises in Castrop-Rauxel in the Ruhr region. A spokesman for the Dusseldorf prosecutors currently leading the investigation confirmed this to dpa hours after two men were arrested at the premises.

A 32-year-old Iranian was suspected of having obtained the toxins cyanide and ricin, the Düsseldorf public prosecutor and Recklinghausen and Münster police said earlier on Sunday. He was arrested along with another man.

The men were lightly clothed as they were led away, with just a jacket thrown over them against the winter cold, eyewitnesses said. They did not offer any resistance.

Ricin is highly toxic and is officially listed in Germany under biological weapons.

The mass-circulation newspaper Bild reported that staff from the federal disease control body, the Robert Koch Institute (RKI) and the Federal Criminal Police (BKA) were involved.

A report on the WDR regional public broadcaster said they were brothers.

The investigators moved in at around midnight on Saturday to search the 32-year-old's lodgings in Castrop-Rauxel, some 15 kilometres north-west of Dortmund. Many were wearing protective suits.

A broad area around the site was cordoned off as a large contingent of police officers, firefighters and emergency services was deployed to the site.

Evidence was placed in blue containers and taken to a decontamination site set up by the fire services, according to a dpa reporter.

"The accused is suspected of having prepared a serious act of violence that is dangerous to the state," investigators said. "The search serves to find corresponding toxins and other evidence."

It has not yet been decided whether the 32-year-old will be brought before a magistrate.

According to Bild, the BKA had been watching the men for days, after receiving a warning from a "friendly intelligence agency."

A previous ricin case in Cologne four years ago, in which a Tunisian man and a German woman manufactured the poison and conducted a trial explosion, resulted in lengthy prison terms.

In that case too, a foreign intelligence agency provided a tip-off after large quantities of the toxin were purchased. The authorities estimated at the time that a bomb packed with steel balls and the ricin could have killed 200 people.