At least 11 people fell ill after an envelope containing an unknown substance was opened at a U.S. Marine base in Virginia on Tuesday, authorities said.
The envelope was opened inside a building at the Joint Base Fort Myer-Henderson Hall in Arlington around 1 p.m., the local fire department said.
"Personnel in the affected building took immediate preventative measures by evacuating the building," the U.S. Marine Corps tweeted.
But at least 11 people nonetheless suffered nose bleeds, sore throats and burning sensations on their faces and hands. Three of them were brought to a nearby hospital in stable condition, Arlington fire officials said.
The U.S. Marine Corps, local law enforcement and the FBI were still investigating late Tuesday.
