Envelope containing 'unknown substance' leaves 11 sick at US military base near Washington

Washington: An envelope containing an "unknown substance" was opened at a US base near Washington on Tuesday, leaving 11 people sick, including military personnel, officials said.The envelope was received at Joint Base Myer-Henderson Hall, leading to an evacuation of the building, the US Marine Corps said in a statement.[caption id="attachment_1402067" align="alignleft" width="380"]

Representational image. Agencies.[/caption]Base officials "are coordinating with local HAZMAT teams and FBI. Several Marines are receiving medical care as a result of this incident," the statement read."No additional details are available at this time as the investigation is ongoing."The Arlington Fire Department tweeted that "11 people started feeling ill after letter was opened in consolidated admin building."CNN reported that a corporal, gunnery sergeant and a colonel complained of a "burning sensation" on their hands and face.Marine spokesman Major Brian Block said it was too soon to say whether the incident was being considered a terror attack."It's way too early to start speculating on any of that, we have to wait and let the investigators do their jobs," Block told AFP.Joint Base Myer-Henderson Hall overlooks Arlington Cemetery just across the Potomac River from Washington.