New York: For over 50 years, journalists, writers and even psychologists have tried to unravel the exact reason why American author Ernest Hemingway took his own life.

Now his close friend and collaborator has claimed that Hemingway may have been driven to suicide, by shooting himself at his Idaho home while his wife Mary slept, because of his surveillance by the FBI, the media reported.

AE Hotchner says he believed the FBI's monitoring of the Nobel Prize-winning author, over suspicions of his links to Communist Cuba, "substantially contributed to his anguish and his suicide" 50 years ago.

He wrote in a daily that Hemingway's concerns, which were dismissed as paranoid delusions, actually had a massive impact on him which "substantially contributed to his anguish and suicide".

Hemingway, who penned 'For Whom The Bell Tolls' and 'The Old Man and the Sea', was terrified of being bugged and followed by the FBI, according to Kotchner. He writes: "I now believe he truly sensed the surveillance, and that it substantially contributed to his anguish and his suicide."

In 1983, the FBI released a 127-page file it had kept on Hemingway since the 1940s, confirming he was watched by agents working for J Edgar Hoover.

Hotchner described being met off a train by Hemingway in Ketchum, Idaho, in November 1960, for a pheasant shoot with their friend Duke MacMullen.

Hemingway, struggling to complete his last work, complained "the feds" had "tailed us all the way" and that agents were poring over his accounts in a local bank that they passed on their journey.

Later that month he was committed for psychiatric care at Mayo Clinic in Minnesota. A few days after returning home, he shot himself in the head with his shotgun aged 61.