LAS VEGAS (Reuters) - An unidentified man is in critical condition with suspected ricin poisoning after staying in a Las Vegas hotel room where the potentially deadly substance was found, police said on Friday.

The FBI said the incident was not thought to be terrorism related.

Police said the man, who they did not name, had last occupied the room two weeks ago and was taken to a local hospital on February 14 when he complained of breathing difficulties.

A suspicious substance, which tests have confirmed to be ricin, was found in the sick man’s room on Thursday after a relative or friend went to the hotel to collect his possessions, Las Vegas deputy police chief Kathy Suey told a news conference.

No one else has reported symptoms and it was not clear where the ricin came from, or what is was doing in the room at the Extended Stay America Hotel in Las Vegas.

Suey said the sick man, in his 40s, “is in critical condition and he is unable to speak with us right now. We have no indication why the ricin was in that room.”

Suey said castor beans, the basis for making ricin, were found in the hotel on Thursday and that the ricin was found in vials in the room.

There is no definitive test for ricin, which in proper doses can be used to treat cancer.

It can be in the form of a powder, a mist or a pellet and can be inhaled or ingested. There is no known antidote and most victims die within 36 hours to 72 hours from exposure to as little as a pinhead amount of the substance.

Police said the investigation was still in its early stages and gave no details about the sick man, nor of the person who visited the hotel on Thursday. They said the visitor was not a suspect.

Six other people, including police and hotel workers, were admitted to the hospital as a precaution on Thursday but no one else has symptoms, Suey said.

Ricin attacks cells, preventing them from making necessary proteins.

The most famous case of ricin poisoning was in 1978 when dissident Bulgarian writer Georgi Markov was killed after a passerby in London jabbed him with an umbrella that injected a tiny ricin-filled pellet.