An Iranian national was arrested in his underwear Sunday after he was reportedly caught trying to deploy biological weapons in northwestern Germany.

The 32-year-old man had allegedly obtained cyanide and ricin in preparation for a “serious act of violence,” investigators said, according to German outlet Welt.

The Iranian and one other man, whose affiliation was not disclosed, were arrested by anti-terror investigators in the former’s Castrop-Rauxel living quarters around midnight.

Both were apprehended in their underpants — and jackets that had only been thrown on as authorities descended on the building, eyewitnesses told Welt.

Investigators wearing protective suits wheeled the toxins and other evidence out of the building in blue barrels and deposited them at a decontamination point set up by the fire department.

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

Police have not disclosed the plans for the alleged attack, how far the plans had progressed or whether the men had chosen a target, but warned it may have been an Islamist assault.

Investigators had been trailing the men for several days, Welt reported.

Ricin is one of the most toxic biological agents known and can be used as an effective airborne weapon, according to the Centers for Disease Control and Prevention. Cyanide, fatal to humans in even the smallest amounts, are also listed on the federal agency’s bioterrorism chemicals page.

Officials are investigating the evidence further before formally filing charges, the outlet reported.