Released Lockerbie bomber Abdel Baset al-Megrahi is seen in a hospital bed in Tripoli on Sunday in this image taken from Britain's Channel 4 News. (Channel 4 News/Associated Press)

Britain's Middle East minister and other officials advised Scotland's government that there were no legal obstacles to releasing Lockerbie bomber Abdel Baset al-Megrahi and returning him to his native Libya, according to correspondence released Tuesday.

The letters, published on British and Scottish government websites, also indicate diplomats explained that the United Kingdom never made a binding promise to the United States to keep al-Megrahi jailed in Scotland.

A separate file of correspondence shows that British Justice Secretary Jack Straw initially believed al-Megrahi should be excluded from a prisoner transfer agreement signed between the U.K. and Libya, but later changed his mind — saying he did not wish to damage the "beneficial relationship" between the two countries.

Al-Megrahi, was the only person convicted of the bombing of Pan Am Flight 103 in December 1988, which blew up over Lockerbie, Scotland. The attack killed 270 people, mostly Americans.

The Scottish government released Al-Megrahi, who has terminal prostate cancer, on compassionate grounds Aug. 20. He arrived home to a hero's welcome.

His release was sharply criticized by victims' families in the United States, President Barack Obama and FBI director Robert Mueller.

The release of the correspondence comes a day after the Sunday Times reported that the British government agreed to include al-Megrahi in a prisoner transfer agreement because it would reflect favourably on Britain at a time when a major oil deal was being negotiated with Libya.

Officials insisted in the Foreign Office letters that only Scotland's government could decide whether to send the convict home, but offered assurance that London did not believe it would breach international law, or risk souring ties with key allies, if Scottish ministers did so.

In a letter sent Aug. 3, British Middle East Minister Ivan Lewis told Scottish Justice Secretary Kenny MacAskill that Britain's government didn't believe returning al-Megrahi home would breach promises made to the U.S. or the United Nations.

"The U.K. government's assessment remains that while the U.S. pressed the U.K. to provide a definitive commitment on the future imprisonment of the Lockerbie accused, the U.K. government of the day declined to do this on the grounds that it did not wish to bind the hands of future governments," Lewis wrote.

He said that at the time of al-Megrahi's 2001 conviction, ministers could "not rule out the possibility that our relations with Libya may one day change, as indeed they have."

In a separate letter sent to Scottish government official George Burgess in July, the Foreign Office told him that Britain "did not give the U.S. an absolute commitment" to keep al-Megrahi jailed in Scotland.

It noted there was no "definitive commitment, legal or otherwise," to prevent al-Megrahi's return.

Doctor says al-Megrahi's health worsening

The Scottish government also released notes from meetings with officials of the Libyan government in which the top medical officer in Scotland's prison service indicated that al-Megrahi's health was worsening.

On May 5, Dr. Andrew Fraser, the prison service's director of health and care, stated that al-Megrahi health was "reassuringly good despite the serious condition he suffers," but also added that as time passed his "condition would deteriorate," the notes said.

But at a July 22 meeting, Fraser said a blood test had been done to assess the activity of the cancer and "it was already clear that the previous treatment was not holding the progress of the disease," the notes said.

They said Fraser advised that a new treatment had been embarked upon, and that al-Megrahi "was experiencing a bit more pain than usual and had been encouraged to take his medication regularly."

On Monday, Libya's secretary of state for foreign affairs, Mohammed Siala, said al-Megrahi's health is failing, and television pictures from Britain's Channel 4 showed him lying in a hospital bed, an oxygen mask on his face.

However, there was no way to independently verify al-Megrahi's condition amid remarks by his father that suggested he is not dying.

With files from The Associated Press