Two Iranian men were detained by German police on Saturday evening after receiving a tip from U.S. security officials that they were plotting an attack, according to Munster police and German press reports. 

Munster police officials said that the two men were suspected of preparing "a serious act of violence" involving cyanide and ricin to "commit an Islamist-motivated attack." 

The two men, ages 25 and 32, were taken into custody in Castrop-Rauxel, a town in Western Germany just outside of Dortmund. 

Ricin is a poison found naturally in castor beans, while cyanide is a deadly chemical that can exist in various forms. 

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The extent of the suspects' plans wasn't immediately known. Investigators wearing hazmat suits searched the house on Sunday, but no toxins were located, according to police. 

The FBI tipped officials off about the planned attack, according to the German newspaper Bild. 

A spokesperson for the FBI declined to comment on Sunday. 

A 31-year-old Tunisian man was convicted in Germany of manufacturing a biological weapon in 2020 after buying thousands of castor beans to produce ricin, then testing it on a dwarf hamster. 

The Associated Press contributed to this report.