The late Pope John Paul was wounded by a knife-wielding priest in 1982, a year after he was shot in St Peter's Square, but the injury was kept secret, his former top aide says in a documentary film.

Cardinal Stanislaw Dziwisz also discloses that when John Paul II was unable to pronounce words several days before his death in 2005, he told his aides that if he could not speak any more the time had come for him to die.

Dziwisz, who is now cardinal of Krakow, Poland, was John Paul's private secretary and closest aide for nearly 40 years, including all of his 27 years as pontiff.

The documentary, called Testimony and narrated by the British actor Michael York, is a film version of a memoir published by Dziwisz last year but with some additions.

It will make its official premiere at the Vatican on Thursday night in the presence of Pope Benedict XVI.

On May 12, 1982, the pope was visiting the shrine city of Fatima in Portugal to give thanks for surviving a first assassination attempt a year earlier on May 13, 1981, when he was shot in St Peter's Square by Turkish gunman Mehmet Ali Agca.

A crazed ultra-conservative Spanish priest, Juan Fernandez Krohn, lunged at the pope with a dagger and was knocked to the ground by police and arrested. The fact that the knife actually reached the pope and cut him was not known until now.