Tunis (AFP) – Tunisian authorities said Friday they had arrested two suspects in connection with a biological bomb plot thwarted by police in Germany in June.

The two men are suspected of links to 29-year-old Tunisian Sief Allah H. who was arrested in Germany in possession of the deadly poison ricin and bomb-making material, the interior ministry said.

German police commandos on June 12 stormed the Cologne apartment of Sief Allah H. and discovered “toxic substances” that turned out to be ricin, according to the German authorities.

Produced by processing castor beans, ricin is lethal in minute doses if swallowed, inhaled or injected and 6,000 times more potent than cyanide, with no known antidote.

Sief Allah H., who has been charged with possession of weapons of war and planning a serious act of violence against the state, was thought to have followed instructions on making a ricin bomb disseminated online by the Islamic State group.

Investigations revealed that one of the two men had conspired with Sief Allah H. “to simultaneously carry out in Tunisia and Germany two attacks using homemade bombs”, Tunisian anti-terrorism spokesman Sofiene Sliti told AFP.

The other suspect allegedly prepared a false passport to help Sief Allah H. flee to other European countries, according to the interior ministry.

Germany remains on high alert after several deadly attacks claimed by the IS group, including a 2016 truck rampage through a Berlin Christmas market by a Tunisian asylum seeker that claimed 12 lives.