UK Home Secretary Jack Straw has defended his decision not to disclose the details of medical tests on former Chilean dictator General Augusto Pinochet, after he was declared unfit for extradition.

Human rights organisation Amnesty International said denying such access to prosecutors seeking the general's extradition raised doubts about the fairness of the whole process.

But Mr Straw told BBC Radio 4's Today programme that it would have been "very unusual" to disclose the details of the tests.

He said: "Plainly it was essential that any medical examination was disclosed to me and also to the UK prosecuting authorities and both of those have happened."

Interviewer John Humphrys asked whether the tests should have been made available to the House of Commons library, but Mr Straw replied: "It's very unusual for medical evidence to be more widely available."

Meanwhile relatives of those who disappeared under military rule in Chile say they will carry on in their campaign to put General Pinochet on trial.

The tests were carried out by four independent clinicians. On the basis of these, Mr Straw said the 84-year-old was unfit to stand trial on torture charges relating to his 1973-90 rule.

Mr Straw announced on Wednesday he was "minded" to allow the general to return home. Interested parties have until next Tuesday to lodge objections to Mr Straw's decision.

Amnesty, the Medical Foundation for the Care of Victims of Torture and Human Rights Watch are consulting their lawyers as to whether there are grounds to mount a legal challenge.

Amnesty said access to the medical report was "essential" for the states requesting extradition, in order for them to "make a submission or consider any other action".

"Seeking representations from the parties without providing them with the medical report and opinion denies natural justice. The process is not transparent or fair," it said.

It also said Mr Straw evaluated the report "in secret", and as a political official, rather than by a court, his decision did not give "any opportunity for the prosecution to observe the medical examination, challenge it or obtain a second independent medical opinion".

However, in its statement, Amnesty added: "We believe that Augusto Pinochet has the same rights as any other person to all legal mechanisms available - including making a legal case that he is unfit to face extradition.

Depression and diabetes

"No individual who is determined by a court to be unfit to participate in an extradition proceeding should have to do so."

General Pinochet's supporters say the general has suffered from depression, a series of strokes, diabetes, and renal and heart problems since being arrested in a London clinic in October 1998 as he lay recovering from a back operation.

But in his Commons statement on Wednesday, Mr Straw hinted that it was a mental rather than physical incapacity which meant the general was unfit to stand trial.

He said the criteria he considered when making the decision included "whether Senator Pinochet would be in a position to follow the proceedings, whether he could give intelligible instructions to those representing him and whether he could give a coherent statement of his own case and recollection".