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A Tunisian man arrested in Germany is suspected of trying to build a biological weapon using the deadly poison ricin, prosecutors said Thursday, according to AFP.

At the same time, they noted there was no indication of any "concrete attack plans."

The 29-year-old, identified as Sief Allah H., was detained after police stormed his apartment in Cologne late Tuesday, where they found unknown "toxic substances" that turned out to be ricin.

"He is strongly suspected of intentionally manufacturing biological weapons," federal prosecutors said in a statement quoted by AFP.

The suspect has been charged with violating German law on the possession of weapons of war, and "preparing a serious act of violence against the state".

However, prosecutors cautioned that it remained unclear whether he was planning to use ricin to carry out an Islamist attack in Germany.

"There are no indications that the accused belongs to a terrorist organization, nor of any concrete attack plans at a certain time or place," they said.

German media reported the police raid came after German intelligence services were tipped off by foreign authorities who had grown suspicious of the suspect's online purchases.

Germany has been on a high level of alert due to a series of terrorist attacks in the country in recent years.

In one attack, a 17-year-old Afghani with an axe attacked passengers on a train in Wurzburg before being shot dead by security forces.

In a second incident, an attacker set off a bomb in a restaurant in Ansbach, killing himself and wounding 12 others.

The worst such attack took place in December of 2016, when Tunisian terrorist Anis Amri killed 12 people and injured dozens more when he drove a truck into a Christmas market in Berlin.

Prosecutors said Sief Allah H. started buying the necessary equipment and ingredients to make ricin in mid-May -- including an online purchase of "a thousand castor seeds and an electric coffee grinder", according to AFP.

He succeeded in manufacturing the toxin earlier this month. The dangerous substance has been secured by the authorities, they added.

Ricin -- a poison that is produced by processing castor beans -- has no known antidote and is one of the world's most lethal toxins.

The case comes less than a month after French authorities said they had foiled a terror attack possibly involving the use of ricin. Two brothers of Egyptian origin were arrested.