The man, who told police the toxic agent did not belong to him, took the powdery substance to the manager's office, and the manager called police.

Lombardo did not elaborate on who the man was.

The man, along with three employees of the long-term stay hotel, were taken to a hospital as a precaution, although they had no signs of being affected by the substance, police said.

Police were not sure about the origin of the substance or why it was in the room. The ricin and castor beans, from which ricin is derived, were found in the suite, although Lombardo did not say how much of the substance was found.

Preliminary tests showed that the substance was ricin, a deadly toxin that can be a powder, a mist or a pellet, according to the Centers for Disease Control and Prevention's Web site. It also can be dissolved in water.

"Ricin is very serious," Lombardo said. "Something the size of the head of a pin can be deadly."

Officials were downplaying the significance of the discovery late Thursday.

Earlier, multiple agencies responded to the incident, including the Clark County Fire Department and the Nevada National Guard.

"This is not a terror incident at this point," Lombardo said.

"We don't know that there was any criminal intent on anybody's part," Las Vegas police Sgt. John Loretto said. "It could have been somebody that was reading a book who wanted to try to make something."

Police cordoned off the area of Valley View between Flamingo Road and Harmon Avenue, and residents at the Extended Stay America were not being allowed back into the building late Thursday.

Residents at an apartment complex north and east of the suites were allowed to come and go.

The last time Las Vegas police dealt with ricin was in 2003, when a 60-year-old former gaming executive and chemist killed himself with the agent.

The man, Tomoo Okada, told emergency responders that he had injected himself with the deadly poison, which prompted two hospital emergency rooms to be shut down for about three hours.

On Thursday, 30-year-old Charlie Aitken, who was visiting Las Vegas from Nova Scotia, Canada, for the first time, said he was told by police to leave his room at the Extended Stay America about 3 p.m.

As he walked out, he saw men suiting up in hazardous materials outfits.

"It was like, 'Welcome to Vegas!,' " Aitken said.

Contact reporter Lawrence Mower at lmower@reviewjournal.com or (702) 383-0440.