Sept. 8, 2010 -- The FBI is concerned that Islamic extremists might attack and retaliate at this Saturday's Koran burning planned by radical Florida pastor Terry Jones, ABC News has learned.

"While the FBI has no information to indicate a specific attack has been planned against the United States or U.S. assets in response to the 'International Burn a Koran Day' event, the FBI assesses with high confidence that, as with past incidents perceived as acts of desecration against Islam, extremist actors will continue to threaten or attempt to harm the leaders, organizers, or attendees the event," an FBI intelligence bulletin notes.

The FBI is concerned not only about the potential for an attack at the event -- but also about retaliation going forward. The Aug. 19, 2010 intelligence bulletin out of the Bureau's Jacksonville field office is entitled, "Extremists Likely to Retaliate Against Florida Group's Planned 'International Burn a Koran Day.'"

The intelligence bulletin states that Jones' advertising of the event drew an immediate response from a known terrorist website frequented by radicals. Postings on the Al-Faloja website included a forum member writing, "I wish to detonate myself in this church now. ... I want to become a martyr and detonate myself in this filthiest filth."

Another member warned, "Oh you Americans, I swear by Allah if you do this deed await a war that you have not witnessed ... we will not rest until we kill tens of you in place of every letter in the book of Allah. ..."

Word of the memo first was posted on the blog Infowars.com. FBI officials would not publicly comment on the intelligence bulletin but confirmed its authenticity.

Though other officials spoke without being named, the FBI spokesman in Jacksonville, Special Agent Jeff Westcott, declined to comment when contacted by ABC News.

However, FBI officials told ABC News that FBI agents from Jacksonville have met with Jones to inform him of the intelligence and potential threat. FBI agents from the Jacksonville field office are planning to have assets at the ready in case of an attack at the church.

The FBI bulletin further observes that INSPIRE, a new online terrorist propaganda magazine, specifically instructs "home-grown extremists to conduct small scale attacks" and "attacks on persons who disrespect symbols of Islam."

The FBI's bulletin notes serious implications of the burnings taking place.

"This attention will most likely have political and national security implications which could involve the boycott of American goods and services, violent demonstrations within the United States and abroad, threats and/or acts of violence from terrorist organizations and/or lone extremist actors, and further segregation between the Muslim and non-Muslim American communities," the bulletin notes.

The FBI suggests history is its troubling guide.

The bulletin cites the recent case of Muslim convert Zachary Chesser, who made death threats against the creators of "South Park" after the program mocked the Prophet Muhammad and notes that INSPIRE mentioned that Molly Norris, a cartoonist who created "Everybody Draw Muhammad Day" should be targeted for killings.

There have been other instances. Dutch filmmaker Theo van Gogh was assassinated in 2004 after he made a controversial film about women living in Islamic countries. Here in the United States, the woman dubbed "Jihad Jane" was part of an alleged conspiracy to kill Lars Vilks, a Swedish artist who drew the Prophet Mohammed with the body of a dog.