A fan holds up a picture of John Lennon at a candlelight vigil on the 25th anniversary of Lennon's death at Strawberry Fields in Central Park in New York City, December 8, 2005. [Photo: Reuters]

The FBI has released the last 10 documents from its secret files on slain Beatle John Lennon that had been withheld for 25 years on the ground they could prompt "military retaliation" against the United States, campaigners for their release said on Wednesday.

The files turn out to contain only well known information about Lennon's ties to left-wing leaders and antiwar groups in London in 1970 and 1971, said Jon Wiener, a history professor at the University of California, Irvine, and the Southern California chapter of the American Civil Liberties Union.

"Today we can see that the national security claims the FBI has been making for 25 years were absurd from the beginning. The Lennon FBI file is a classic case of excessive government secrecy," Wiener said in a statement.

The released documents include one that states Lennon "encouraged the belief that he holds revolutionary views ... by the content of some of his songs."

Another talks of the Beatle turned anti-war campaigner promising to finance a left-wing bookshop in London. A third describes a 1971 interview with Lennon in The Red Mole, a London underground newspaper, in which the singer "emphasized his proletarian background and his sympathy with the oppressed and underprivileged people of Britain and the world."

Wiener first requested the files in 1981. After legal action under the U.S. Freedom of Information Act that went all the way to the Supreme Court, he got most of the 300 pages in the Lennon files released in 1997.

But 10 documents remained classified on the grounds of national security. The FBI told the U.S. courts in 1983 that release of those documents could "lead to foreign diplomatic, economic and military retaliation against the United States."

Wiener, whose campaign was detailed in a book and formed the basis of the 2006 documentary "The U.S. vs John Lennon," has posted the documents on the Web site www.LennonFBIfiles.com.

"I doubt that Tony Blair's government will launch a military strike on the U.S. in retaliation for the release of these documents," Wiener said.

Lennon, whose iconic song "Imagine" has become a rallying call for anti-war activists around the world, was murdered in New York in December 1980 by a deranged fan.