Obama’ counter-terrorism adviser calls for Megrahi ‘to be returned to Scotland’

"We've expressed our strong conviction that Al Megrahi should serve out the remainder – the entirety – of his sentence in a Scottish prison,” he was quoted as saying.

He also criticised the "unfortunate and inappropriate and wrong decision."

Brennan was speaking on the first anniversary of al Megrahi’s release from a Scottish prison on 20 August 2010 last year on compassionate grounds.

New Jersey Senator Robert Menendez, claimed that a "cloud of suspicion" hung over the decision to release Megrahi, who had now living with his family in the Libyan capital of Tripoli.

However, Andrew Fraser, the prison doctor whose role it was to compile and present a prognosis based on Megrahi's medical notes, has insisted that he had followed a process of "complete integrity".

It emerged a week ago that the 58-year-old bomber had embarked on a new course of chemotherapy which could extend his life well into 2011.

The fact that Megrahi had lived so long in Libya had incensed many of the US relatives of those who had died in the bombing in December 1988 when Pan Am Flight 103 exploded in mid air over Lockerbie, Scotland, killing 243 passengers, 16 crew and 11 people on the ground.

Menendez was one of four US senators who had written to Scottish First Minister Alex Salmond and British Prime Minister David Cameron laying out the areas where, according to them, "questions linger".

The information requested in the correspondence related to Megrahi's medical diagnosis and communications between BP and the British government.

US politicians wanted to investigate claims that the bomber's release was linked to an oil deal, a suggestion that had been “strongly denied” by all parties involved.

"Every new piece of evidence builds on to the cloud of suspicion hanging ominously over the circumstances surrounding Al Megrahi's release," he claimed.

The Conservative-Lib-Dem government has since described the decision as a "mistake" and opponents at the Scottish assembly called for the publication of further medical evidence.

But Salmond has defended the Scottish government's actions. "The senators' latest letter is totally wrong in saying commercial influences played any role whatever in the decision, and is quite misleading – we have published everything we can, and the senators embarrass themselves by asking us to un-redact material which we are only prevented from publishing because the US government refused permission,” a spokesperson for the Scottish First Minister insisted.

"None of the issues raised in any way alters the fact that the decisions of the Scottish Government were made with total integrity, and according to the due process of Scots Law," the spokesperson concluded.