ABC News' Bret Hovell, Jason Ryan and Barbara Garcia Report: At least five people were exposed to a suspicious white powder at the Denver, CO, headquarters of the John McCain presidential campaign Thursday.
A staffer opened an envelope that had been sent to the campaign which contained white powder and a threatening letter. The office has been evacuated.
"As a precautionary measure we have closed the office and staff are being examined by medical personnel," said McCain campaign spokesman Tucker Bounds.
The campaign says there were between five and ten people in the office at the time, and that they were taken to a hospital to get checked out.
So far no details have been released about the threatening letter.
The Arapahoe County Sheriff’s office is working in conjunction with the Secret Service, the FBI and HAZMAT teams.
Denver is the site of the Democratic National Convention, which will open on Monday.