INEZ, Ky. (WSAZ) -- Three guards at the Big Sandy Federal Prison in Inez were assaulted by four inmates during a routine search of an inmate housing unit.

Philip Heffington, a Bureau of Prisons spokesperson, tells WSAZ.com that the incident happened about 2:00 p.m. Sunday. He says additional staff responded and quickly contained the situation.

Heffington says the three guards were taken to a local hospital for treatment and later released. He says the four inmates involved in the assault were not hurt.

The prison was placed in lock down following the incident.

The F.B.I. was notified and an investigation into the incident is underway.