WASHINGTON – An envelope containing an “unknown substance” was opened at aUS base near Washington on Tuesday, leaving 11 people sick, includingmilitary personnel, the Marine Corps said.

The envelope, which was received at Joint Base Myer-Henderson Hall around3:30 pm (2030 GMT), led to an evacuation of the building, the US MarineCorps said in a statement.

“Shortly after receiving the letter, 11 people started to feel ill,” threeof whom were “transported in stable condition for further medicalevaluations,” it said.

“Joint Base Police Department officials are working with local HAZMATteams, NCIS (Naval Criminal Investigation Service) and the FBI. Thebuilding was screened and cleared,” it said.

CNN reported that a corporal, gunnery sergeant and a colonel complained ofa “burning sensation” on their hands and face.

Marine spokesman Major Brian Block said it was too soon to say whether theincident was being considered a terror attack. “It’s way too early to startspeculating on any of that, we have to wait and let the investigators dotheir jobs,” Block told AFP.

Joint Base Myer-Henderson Hall overlooks Arlington Cemetery just across thePotomac River from Washington. – APP/AFP