Colorado ? A threatening letter containing an unidentified white powder was sent to a John McCain campaign office in Centennial, a south Denver suburb, Thursday, authorities said. No injuries were immediately reported.

A second letter sent to a McCain campaign office in New Hampshire initially was reported to contain threatening language and white powder. Authorities said that was a false alarm and there was no powder in that envelope.

At least 19 people were examined at hospitals or were quarantined outside the Colorado office while authorities tried to determine whether the powder was hazardous, but everyone was sent home by late Thursday, said Arapahoe County Sheriff Grayson Robinson. He said the substance was not hazardous and not lethal, but that it will take days before they determine what it was.