The US senate committee examining the release of the convicted Lockerbie bomber is calling for his medical records to be released.
It comes after Scottish Labour demanded the publication of the evidence which led to Abdelbaset Ali al-Megrahi being given less than three months to live.
Megrahi was released on compassionate grounds in August last year.
The Scottish government confirmed it had received the letter and would reply "in due course."
Ministers have already published a report which led to the decision to release the Libyan.
The report, published by the Scottish Prison Service's medical chief, Dr Andrew Fraser, suggested last August that Megrahi - who has terminal prostate cancer - had three months to live.
Labour said the medical advice which led Dr Fraser to his conclusion should be published, along with the names of the doctors who provided it.
And now the US senators have written to First Minister Alex Salmond asking the Scottish government to provide the full medical information or to request Megrahi's permission to release the information, if such permission is necessary.
In addition, the senators asked the Scottish government for the names, medical training and specialisations of the doctors who examined Megrahi.
"We understand that an extensive medical record was used as the basis of the decision to release Mr al-Megrahi, but only one three-page medical document with redactions has been released by the Scottish government," the senators wrote.
"Independent examination of Mr al-Megrahi's complete medical record is necessary in order to understand the circumstances surrounding his compassionate release.
"A more complete medical record may help us understand exactly what Mr al-Megrahi's treatment options were and thereby help clarify questions about his prognosis."
The Scottish Labour Party have pointed to a study in the Journal of Clinical Oncology from 2008, which claimed patients with advanced metastatic prostate cancer that is resistant to hormone treatment had a median life expectancy of 19.2 months from the start of chemotherapy.
Labour's community safety spokesman James Kelly said it was time for Scottish Justice Secretary Kenny MacAskill to release the "full facts" surrounding the medical evidence for Megrahi's release.
He added: "We know that Megrahi intended to start chemotherapy - he indicated that in his application for release.
"It's now time for the full facts to come out."
But a Scottish government spokeswoman said: "Dr Fraser drew on expert advice from a number of cancer specialists in coming to his clinical assessment that a three-month prognosis was a reasonable estimate for al-Megrahi - it was not based on the opinion of any one doctor.
"These specialists included two consultant oncologists, two consultant urologists and a number of other specialists, including a palliative care team, and Mr Al-Megrahi's primary care physician."
She added that three doctors were also hired by the Libyan authorities to assess Megrahi, namely Ibrahim Sherif, Karol Sikora and Jonathan Waxman.
However, the spokeswoman said their examinations formed no part of the expert advice considered by Dr Fraser.
Last month, the Conservatives said the advice of other doctors and medical experts who examined Megrahi should also be released.
The US senators recently launched an inquiry into the release of Megrahi, the only man convicted of the 1988 bombing of PanAm flight 103 which killed 270 people.
Scottish government ministers and former UK Justice Secretary Jack Straw rejected calls to appear before the US inquiry.
The head of the Roman Catholic church in Scotland, Cardinal Keith O'Brien, hit out at the US "culture of vengeance" over the issue at the weekend.