WASHINGTON (AP) — Three people at a northern Virginia military base were transported to a medical facility and were in stable condition Tuesday after a suspicious piece of mail was opened and nearly a dozen people felt ill.

A spokeswoman for Joint Base Myer-Henderson Hall said people in the office on the Marine Corps side of the base had reported that as soon as the mail was opened they began feeling poorly and complaining of sore throats.

Leah Rubalcaba said 11 people were initially assessed, and three were transported for medical care.

The Arlington County Fire Department said on Twitter that the three are stable and the investigation is ongoing.

The Marine Corps said the building was evacuated, and several Marines are receiving medical care. The Corps said the Naval Criminal Investigative Service and the FBI are conducting a joint investigation.

The joint base is across the Potomac River from Washington, D.C., bordering Arlington National Cemetery.

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