FBI agents nationwide have been ordered to conduct "threat assessments" of inmates who may have become radicalized in prison and could commit extremist violence upon their release, according to an FBI (search) letter obtained by The Associated Press.

"The primary goal of these efforts is to assess and disrupt the recruitment and conversion of inmates to radicalized ideologies which advocate violence," according to a letter from the acting assistant chief of the FBI's Los Angeles office, Randy D. Parsons (search).

The agency has been trying to identify potentially disruptive groups for "some time," according to the letter. "However, recent investigations have identified a clear need to increase the FBI's focus and commitment in this area," Parsons wrote in the letter, which was dated Friday and obtained Tuesday by the AP.

He said the FBI wants to increase its efforts to "identify, report, analyze and disrupt efforts by extremist persons or groups to radicalize, recruit or advocate for the purpose of violence within correctional facilities."

California prison officials confirmed receiving the letter.

The order comes as an investigation continues into whether a suspected Southern California terror plot originated in a state prison in Folsom, near Sacramento. Three Los Angeles area men, including a parolee from California State Prison, Sacramento, are suspected of plotting attacks on Jewish and National Guard sites.

FBI director Robert Mueller (search) warned the Senate Intelligence Committee in February that prisons are "fertile ground for extremists," but FBI officials had declined to disclose steps they were taking.

Karen Ernst, a spokeswoman for the FBI's Sacramento office, confirmed her office is participating in the "threat assessments."

Telephone messages left with the FBI in Washington were not immediately returned.

"The FBI will be going into each institution and assessing each population," said Todd Slosek, spokesman for the California Department of Corrections and Rehabilitation.

He expects the FBI to examine the department's information on all "disruptive groups," including prison gangs and Islamic organizations.

That shouldn't interfere with inmate religious practices, free speech or other rights, Parsons wrote in the letter.

Authorities said they believe the Southern California plan originated in a shadowy group at the Folsom prison known as Jamiyyat Ul Islam Is Saheeh.

The Southern California case arose after 25-year-old Levar Haley Washington and another man were arrested July 5 by police in Torrance, a suburb southwest of Los Angeles, for investigation of robbing gas stations.

Authorities have said they suspect a list found in Washington's Los Angeles apartment contained potential terrorist targets, although Washington has not been charged with a terrorism-related crime. The list included National Guard recruiting stations, synagogues and the Israeli Consulate.

Washington converted to Islam in the Sacramento-area prison before his parole in November.