BERLIN (Reuters) - A 29-year-old Tunisian arrested last week on suspicion of producing the lethal toxic ricin was in contact with radical Islamists, and twice tried unsuccessfully to reach Islamic State in Syria, Germany’s top federal prosecutor said on Wednesday.

Peter Frank, head of the GBA Federal Prosecutor’s Office, told broadcaster SWR that the man, Sief Allah H., was not currently believed to have been a member of Islamic State, but was deeply involved with the Islamist scene.

“He was deeply anchored in the Islamist spectrum and was in contract with people from this spectrum,” Frank told the broadcaster.

The man was arrested in Cologne on suspicion of planning an Islamist-motivated attack and building a “biological weapon” with ricin, a poison found in castor beans.

The GBA on Wednesday said 3,150 grains of ricin - all ordered via the Internet - were seized during a search of the suspect’s home, along with 84.3 mg of prepared ricin.

German broadcaster ARD said even one ricin grain could be deadly for a child.

No comment was immediately available from prosecutors on the significance of the amount of ricin found. The number of ricin grains found were triple the amount initially reported by GBA.

Frank said the evidence at the scene indicated that the suspect was considering building an explosive device, but no possible target or timetable had been determined.

It was the first time Germany had dealt with a possible attack with a biological weapon, Frank said, although Islamist militants had discussed such an attack for some time in their communications.

“Islamist terrorists have repeatedly promoted diverse instructions, including for production of ricin from ricin grains, on their advertising channels,” Frank told SWR.

The case has fanned concerns about a possible Islamist attack using the lethal toxin after a similar case in France last month.

A source in Germany’s BfV domestic intelligence service said Islamists could stage such an attack in Germany at any time. Islamic State militants had experimented with ricin in the past and had also manufactured it, the source said.

Holger Muench, president of the Federal Criminal Office, told the broadcaster RBB-Inforadio in a separate interview that the Tunisian suspect had manufactured ricin and objects were found in searches that could be used to make a bomb.

GBA said the investigation showed the suspect had been in touch with people from the “radical Islamist” community, but investigators were still trying to determine if those people were themselves members of a militant group.

It said investigators also found 250 metal bearings, two bottles of acetone nail polish remover, wires and 950 grams of a grey powder that contained aluminium and explosive materials from fireworks.