Federal officials say they oversaw a test this week of a jamming technology some hope will help combat the threat posed by inmates with smuggled cellphones.

Department of Justice officials tell The Associated Press the test took place over the course of five days at a maximum-security prison in South Carolina. Assistant Attorney General Beth Williams says it's the first time federal officials have collaborated with officials at a state prison for such a test.

The test marks progress on the state-level quest to stamp out cellphones, which officials have long said represent the top security threat within their institutions.

Jamming technology was tested last year at a federal prison, but a decades-old law says state or local agencies don't have the authority to jam the public airwaves.