CENTENNIAL, Colo. (AP) -- Authorities say a threatening letter containing an unidentified white powder was sent to a John McCain campaign office in the Denver suburb of Centennial, and a similar letter was sent to a McCain office in Manchester, N.H.

A hazardous materials team was trying to determine if the powder found in Colorado is harmful.

It wasn't immediately known if the New Hampshire letter also contained a powder, said Jeff Sadosky, a spokesman with McCain's national campaign office in Arlington, Va.

Andy Lyon of Parker South Metro Fire Rescue Authority said a worker at the Colorado office discovered the power after opening the letter Thursday afternoon.

Lyon said no injuries have been reported.

Seven people drove themselves to Sky Ridge Medical Center, but none showed any symptoms of exposure to a toxic substance, said hospital spokeswoman Linda Watson.

Postal Inspector Jo Jan Henderson said agents from her office are on the scene.

Officials with the FBI, Secret Service and the Arapahoe County Sheriff's Department did not immediately return telephone calls.

The threat came four days before the Democratic National Convention opens in Denver.

(Copyright 2008 by The Associated Press. All Rights Reserved.)