By David Shepardson

WASHINGTON U.S. government offices in the Washington area closed early on Monday due to a severe storm threat and tornado watch that was disrupting air travel.

The National Weather Service said the Washington, D.C., area was under a tornado watch until 9 p.m. ET (0100 GMT Tuesday) with significant threats of locally destructive straight-line winds. Libraries, museums, the National Zoo, pools and other municipal and federal services in the Washington area were also closing early. The U.S. Office of Personnel Management said federal employees must depart no later than 3 p.m.

The tornado watch covers Maryland, Washington and much of Pennsylvania and Virginia.

FlightAware, a flight tracking site, said more than 1,100 U.S. flights had been canceled, including 75 at Washington Reagan National Airport, or 17% of flights. Another 4,100 U.S. flights have been delayed.

(Reporting by David Shepardson; Editing by Lisa Shumaker)