Five mail facilities that handle mail for the Pentagon were closed in the Washington area on Tuesday due to the possible release of anthrax. A remote mail delivery facility operated by the defence department just outside the Pentagon had at least one "positive detection" of anthrax, according to a statement from the defence department. The operation was closed down early Monday. Three other facilities leased by the defence department in Fairfax County, Virginia, which is near the Pentagon, were closed down after a biological detector sounded an alarm later Monday afternoon, county officials said. And a fifth facility - a U.S. Post Office on V Street Northeast in the District of Columbia (D.C.), across the Potomac River from the Pentagon - was closed Tuesday because it is the "upstream" post office for the Pentagon, said Lela Abrar, spokesperson for the D.C. health department. "Upstream" means much of the Pentagon-bound mail comes through the V-Street building before being forwarded to the Pentagon mail facilities. The 250 workers at the D.C. facility would receive a "short course of antibiotics" Tuesday afternoon, Abrar said in a phone interview. --More 2320 Local Time 2020 GMT