The agency said further testing was being conducted on the substance, but it is "within normal values."
White powder also was found in a letter sent to former New York City Mayor Rudolph Giuliani's business in New York City, where police said preliminary tests showed it posed no threat.
A federal law enforcement official, who wasn't authorized to comment publicly and spoke on condition of anonymity, said powder from one envelope tested positive for baking soda. It's not clear where that letter was sent.
Hackensack University Medical Center received a number of people for evaluation because they came in contact with the letters, but a hospital spokeswoman said there were no reported illnesses or injuries.
In New Jersey, the suspicious mailings went to at least five hotels, Carlstadt Police Detective John Cleary said.
The mailings arrived at an Econo Lodge in Carlstadt, a Homestead Suites hotel in East Rutherford and a Renaissance Inn in Rutherford, Cleary said. Investigators intercepted additional envelopes from a mail truck before they reached a Holiday Inn Express and Hampton Inn in Carlstadt, he said.
At the Homewood Suites, General Manager Thomas Martucci said the letter sent to his motel contained yellow powder and a typed letter inside referencing al-Qaida and the Dallas FBI.
"It was nonsense," he said.
Lauren Wallace, a jet company employee from Los Angeles staying at the Homewood Suites, said she saw hazardous-material trucks outside and was shooed back from the lobby to her room around 11:15 a.m. by a hotel employee. She said she was allowed out of her room about 40 minutes later.
Police were called to Giuliani's firm near Rockefeller Center after a worker opened the suspicious letter addressed to Giuliani around 10:30 a.m. Friday, police said. Eight mailroom workers underwent decontamination as a precaution.
A representative for Giuliani's firm said the substance was found to be nonhazardous.
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