Lord Fraser of Carmyllie QC was Scotland`s Lord Advocate when the prosecution was launched against Abdelbaset Ali Al Megrahi in November 1991.

FBI director Robert Mueller has written to Scottish Justice Secretary Kenny MacAskill condemning the decision to free cancer victim Megrahi on compassionate grounds.

But Lord Fraser said he was "appalled" by the head of the FBI's outspoken attack.

And he said he would be writing a personal letter to Mr Mueller to invite him to Scotland to "break bread and discuss some good whisky".

Lord Fraser said: "As a former Lord Advocate I'm quite appalled that the head of the FBI, Robert Mueller, should have set his face so openly against Scotland.

"Bob has been a pro-Scotland nut.

"When he drives in to work he listens to pipe music and it shocks me that he has become so disillusioned with us that he now rejects us as pro-terrorist.

"We are not and he knows that from his regular visits to Edinburgh."

Former First Minister Henry McLeish also criticised Mr Mueller.

He said: "The intervention of the director of the FBI was totally out of order.

"It would be the equivalent of the Metropolitan police chief writing to Barack Obama to complain about a decision."

He said Mr Mueller's criticism is "ill-informed", and added: "Quite frankly, it's none of his business.

"He has a view - fine.

"But that was a slur on the Scottish criminal justice system that we did not deserve."

Since the release, Mr MacAskill has been criticised for his decision, particularly from relatives of Americans killed in the bombing.

Mr Mueller, who was the US assistant attorney general responsible for the Lockerbie investigation, said he was outraged by the decision which made a mockery of the grief of the victims' families and undermined the rule of law.

In the letter to Mr MacAskill, Mr Mueller wrote: "Your action in releasing Megrahi is as inexplicable as it is detrimental to the cause of justice. Indeed your action makes a mockery of the rule of law," he wrote.

"Your action gives comfort to terrorists around the world who now believe that regardless of the quality of the investigation, the conviction by jury after the defendant is given all due process, and sentence appropriate to the crime, the terrorist will be freed by one man's exercise of 'compassion'."

Megrahi, who has always claimed his innocence, served just seven years, five months and four days of his sentence in Scotland for the bombing of the Pan Am jet over Lockerbie in 1988, which left 270 people dead.