Ono claims Lennon was the one real rebel in the Beatles

John Lennon was the only Beatle who cared about campaigning for peace while he was a member of the group, according to Yoko Ono.

In an interview marking the release of a documentary about the FBI's monitoring of Lennon during his time in the US, his widow says they were drawn together by their natural rebelliousness - something he did not share with other members of the band.

"He is the only one who really wanted to do something about [the Vietnam War] when he was a Beatle," she said. "One thing that brought us together was the fact that both of us were rebels in so many ways."

Ono's interview coincided with the premiere last weekend at the Venice Film Festival of The US vs John Lennon. His widow co-operated with the film-makers, David Leaf and John Scheinfeld, and gave them access to rarely seen amateur film footage from 1966 to 1976 - a period when Lennon was convinced the FBI was watching him.

He was right. Almost 20 years after his murder in 1980, the government released the FBI files on Lennon, which ran to more than 280 pages. One document received by the FBI from the CIA detailed that Lennon planned to take part in a protest at the 1972 Republican National Convention.

At the time, the South Carolina Senator Strom Thurmond seized on the revelations and asked President Nixon's Attorney General to terminate Lennon's visa. A few weeks later, Lennon was given 30 days to leave and was told his visa had been terminated because of a drug arrest in Britain.

"I think the world really loved the Beatles for being charming and sweet," Ono said. "But some people did resent the fact that they were no more the sweet, nice, charming boys."

Ono and Lennon fought to stay in the US, and in 1975 they won. He obtained a Green Card allowing him to stay and work. The judge wrote that the musician's battle to stay was "testimony to his faith in the American dream".