SAN FRANCISCO -- A day after the Federal Bureau of Investigation raided a Russian Hill apartment suspected of containing explosive materials, the agency asked the public to help find the man who lives there.

Investigators are looking for 42-year-old Ryan Kelly Chamberlain II, said FBI spokesman Peter Lee.

The San Francisco man is wanted on suspicion of possessing explosive materials and is considered armed and dangerous, Lee said.

Authorities say that anyone who sees the suspect should call 911 immediately, and stay away from him.

"Law enforcement officers will respond and they've been advised to proceed with extreme caution," he said.

Ryan Kelly Chamberlain II, 42, of San Francisco
Ryan Kelly Chamberlain II, 42, of San Francisco (Source: Federal Bureau of Investigation)

Authorities describe Chamberlain as a white man, 6 feet, 3 inches tall and weighing 225 pounds, with brown hair and blue eyes, Lee said Sunday at the FBI's San Francisco office.

Chamberlain was last seen south of San Francisco, wearing a dark blue, hooded sweatshirt and blue jeans, the spokesman said.

He drives a white 2008 Nissan Altima with either Texas or California license plates. The Texas plate number is: BX9M042. The California plate number is: 7FQY085.

"As of right now, we believe he's alone in the vehicle and on the road," Lee said. "We have no indication where he's headed."

The FBI's announcement came a day after authorities and hazardous materials crews conducted an all-day search of Chamberlain's San Francisco apartment.

The FBI has not said what was found during the raid, but Lee said Sunday that "someone with that type of material, bomb-making material ... should be considered armed and dangerous."

Earlier media reports saying investigators found ricin -- a deadly poison -- during the search were not true, Lee said.

"There is no threat to public safety at this time," he said. "We do not believe or can conclusively say there was any type of ricin in the apartment."

Ryan Kelly Chamberlain II, 42, of San Francisco
Ryan Kelly Chamberlain II, 42, of San Francisco (Source: Federal Bureau of Investigation)

Investigators are not sure whether the suspect has firearms or explosives in his car, Lee said.

Tips to the suspect's whereabouts can be submitted at tips.fbi.gov, or by calling the FBI's San Francisco office at 415-553-7400. All calls are confidential, according to the FBI.

Contact Chris De Benedetti at 510-353-7011. Follow him at Twitter.com/cdebenedetti.