Britain's Foreign Office advised Scotland that there was no legal barrier — or promise to the United States — that would prevent it from returning the Pan Am Flight 103 bomber to his native Libya, newly released documents show.

Diplomats explained that Britain had never made a binding promise to the U.S. to keep Abdel Baset al-Megrahi jailed in Scotland, according to a letter that was published Tuesday.

Al-Megrahi, who has terminal prostate cancer, was freed on humanitarian grounds and allowed to return to Libya last month. He had been serving a life sentence in Scotland for the 1988 bombing that killed 270 people, most of whom were Americans, over the town of Lockerbie.

The Foreign Office told Scotland's government that ministers "did not give the U.S. an absolute commitment" to keep al-Megrahi jailed.

Officials said only Scotland's government could decide whether to send the terrorist home, but noted there was no "definitive commitment, legal or otherwise," to prevent it.

Click here to read the documents.

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The Scottish government told FOX News Tuesday that the U.S. government refuses to allow them to release details of any communication between Scotland and the U.S. over al-Megrahi's release.

A source with the Scottish government, speaking on condition of anonymity, said the demand was made in a letter sent Tuesday from U.S. Embassy Chief of Mission Richard LeBaron.

The U.K. and Scottish governments are making public their correspondence on al-Megrahi's release; Prime Minister Gordon Brown insists his government played no part in the decision to let the murderer return to Libya.

The moves follow weekend media claims that the British government struck a deal with Libyan authorities to include al-Megrahi in a prisoner transfer agreement because that was considered to be in Britain's interests at a time when a major oil deal was being negotiated.

Brown told the Financial Times the decision to release al-Megrahi rested with the Scottish government in Edinburgh. He also said he told Libyan leader Muammar al-Qaddafi at the Group of 8 meetings in Italy in July that his administration had no role in the matter.

"I made it absolutely clear to him then that this was not a decision, the future and fate of Mr. al-Megrahi, that we as the United Kingdom could take," the newspaper quoted Brown as saying. "It was a matter for the Scottish Executive, and it was their decision, and their decision alone, that would decide it."

The Sunday Times, citing leaked correspondence between Justice Secretary Jack Straw and his Scottish counterpart, Kenny MacAskill, said the decision not to exclude al-Megrahi from a prisoner transfer agreement — as had originally been requested by Scotland — was made as "wider negotiations" with the government of Libya continued.

Straw immediately dismissed as "simply untrue" any suggestion that economic considerations had an effect on the decision to release al-Megrahi.

Al-Megrahi's release was sharply criticized by victims' families in the United States, President Obama and FBI Director Robert Mueller.

Writing in Tuesday's editions of The Times, opposition Conservative leader David Cameron said the decision to release al-Megrahi "has crossed continents and damaged our relationship with our closest ally, America. It has been a fiasco." Cameron said British ministers need to reveal the extent of their conversations with both the Libyan and Scottish governments.

There has been no direct contact between Obama and Brown over the issue, but Brown is due to speak with Obama in the coming days, Downing Street spokesman Simon Lewis said.

While Brown's government in London is responsible for Britain's foreign relations, the decision about whether al-Megrahi would be released rested solely with the Scottish government.

A spokesman for the Scottish executive said on condition of anonymity that Edinburgh intended to make public minutes of a meeting between al-Megrahi and MacAskill, plus prison and parole board reports and letters from victims' families.

Brown's office said not all correspondence between Libya and Britain would be released — only documents deemed to be relevant by the British or Scottish governments.

No documents related to ex-Prime Minister Tony Blair's trip to Libya in 2004, a visit that marked the end of Qaddafi's international isolation, would be included in the bundle being made public, Brown's office said.

Minutes of Brown's meeting with Qaddafi on the sidelines of the G-8 summit in Italy in July also won't be disclosed.

Al-Megrahi, the only person convicted in the Lockerbie bombing, and MacAskill decided last month that he would be released on compassionate grounds, rejecting the option of sending him home under the prisoner transfer agreement.

Compassionate release is a standard part of Scottish justice for dying prisoners.

Libya's secretary of state for foreign affairs said al-Megrahi's health was failing, and television pictures in Britain showed him lying in a hospital bed, an oxygen mask on his face.

"He is in the hospital, he is a dying man. It is normal then he came to spend his last few days in Libya," Mohammed Siala, a Libyan official, told The Associated Press.

There was no way to independently verify al-Megrahi's condition, and Siala offered no further details.

Al-Megrahi was thoroughly examined by top British doctors before his release, but questions have been raised the seriousness of al-his condition following remarks by his father that suggested he was not dying.

FOX News' Jonathan Hunt and the Associated Press contributed to this report.