EXPLOSIVE tapes on the secret life of Princess Diana will prove that she was pregnant and intended to marry Dodi Al Fayed, it was claimed last night.

American secret agents regularly monitored Diana's conversations and collated 1,000 secret documents using its "spy in the sky", the National Security Agency.

They were obtained by its Echelon satellite surveillance system and contain highly sensitive material including her marriage plans, her views on Prince Philip, who was known to be highly critical of her, and new details of her love affair with James Hewitt. Now, lawyers acting for Mohamed Al Fayed are trying to obtain the tapes through America's Freedom of Information Act.

They hope to present the evidence at Diana's inquest, which is expected to take place next year.

The covert monitoring was controlled from the ultra-secret NSA base at Menwith Hill in the north of England during the last weeks of Diana's affair with Dodi.

A spokesman for Dodi's father, Mohamed Al Fayed, the millionaire owner of Harrods, said: "Mr Al Fayed believes that those intercepts will reveal conversations in which Princess Diana discussed her engagement to Dodi and her pregnancy.