Dec 20, 2006
The documents contain new details about Lennon's ties to left-wing and anti-war groups in London in the early 1970s.
Historian Jon Wiener told the LA Times they showed Lennon rebuffed UK leftists who asked him to fund a bookshop.
Mr Weiner worked for 25 years to obtain the papers despite the FBI claiming they could compromise another country's security services.
In 1972, Lennon led a campaign for peace with his famous "bed-ins" to protest against the Vietnam war.
This made him a target for US authorities, who used wire-taps and surveillance to gather information on the ex-Beatle.
The new documents note an interview with left-wing publication Red Mole and his support for Cambodia following US attacks.
But they also admit Lennon "apparently resisted the attempts of any particular group to secure any hold over him".
Mr Wiener first requested the documents in 1981, several months after he decided to write a book about Lennon following the singer's murder.
Some files were released but the FBI said others were exempt from freedom of information laws.
Mr Wiener sued the US government and received a number of files in 1997 as part of a settlement with the FBI.
Justice Department lawyers continued to withhold the final 10 pages until a federal judge ordered their release.
The FBI had argued making the secretly obtained information public could lead to diplomatic, political or economic retaliation against the United States.
"I doubt that Tony Blair's government will launch a military strike on the US in retaliation for the release of these documents," Mr Wiener told the newspaper.
"Today, we can see that the national security claims that the FBI has been making for 25 years were absurd from the beginning."
The previously released files showed the FBI closely monitored Lennon from 1971-72.