A Tunisian man arrested in Germany in possession of the deadly poison ricin and bomb-making material was planning a biological attack, the national police chief said yesterday.

"Very concrete preparations had been made for an act with a ... biological bomb, which is a first for Germany," Holger Muench, head of the Federal Criminal Police Office, told public broadcaster ARD. German police commandos on June 12 stormed the Cologne apartment of the 29-year-old Tunisian migrant identified as Sief Allah and discovered "toxic substances" that turned out to be ricin.