NEW IBERIA - Authorities shut down the New Iberia Post Office after sheriff's investigators said they found a threatening letter with an unknown substance inside.

Capt. Richard Fleming with the Iberia Parish Sheriff's Office said the threatening letter contained a powdery substance, which led postal officials to evacuate the office.

Fleming said their investigators and the New Iberia Fire Department are assessing the scene at this time. They expect the post office to stay closed for several hours while they clear the scene.