The United States is making high-level appeals to Scottish authorities against the release of a Libyan man convicted in the 1988 Lockerbie airliner bombing. Scotland's justice minister is reported to be preparing to order the Libyan's release next week on humanitarian grounds but U.S. officials say there are compelling reasons why he should stay in prison.

Officials here say Secretary of State Hillary Clinton has joined senior U.S. officials including Attorney General Eric Holder in pressing Scotland not to release the Libyan, who is held responsible for the deaths of 270 people, mostly Americans, in the 1988 bomb attack on the U.S. Pan Am jumbo jet.

The State Department said Clinton, who ended an Africa trip Friday, telephoned Scottish Justice Secretary Kenny MacAskill to add her voice to a list of U.S. officials lobbying against the early release of jailed Libyan intelligence agent Abdelbaset al-Megrahi, said to be terminally ill with prostate cancer.

The Scottish justice chief has been reviewing the case and is widely reported to be prepared to order the Libyan's release next week on health grounds.

Al-Megrahi was found guilty of the airliner bombing by a special Scottish court convened at the Hague in 2001 and given a life prison sentence under which he is eligible for release after 27 years.

The prospect of his early release has angered families of the victims of the bombing, many of whom were American college students returning from studies in Europe. At a news briefing Friday, Assistant Secretary of State for Public Affairs P.J. Crowley said the case for keeping al-Megrahi behind bars is compelling.

"We think that there are compelling reasons, given the tragedy that affected the United States and affected the United Kingdom. Obviously our interest is justice, and our interest is the commitment that we made to the families that we would not only find the perpetrator of this terrorism act, but bring him to justice." Crowley said. "Working with the United Kingdom and with Scotland, he was brought to trial. He had a fair trial. He was convicted. He's serving his time. And we think he needs to stay in jail."

Crowley said while the Scottish regional government has jurisdiction, the Obama administration has also raised its concerns with British authorities and with the government of Libya, with which the United States has had a rapprochement in recent years.

A four-member delegation of U.S. Senators visiting Libya this week also discussed the issue with the Tripoli government.

Senator John McCain, the Republican candidate in last year's U.S. presidential election, said the legislators are "resolutely opposed" to al-Megrahi's release.

Fellow Senator Joseph Lieberman warned of damage to bilateral relations if the Libyan is freed. The senators met Friday with Libyan leader Muammar Gadhafi

The long-troubled U.S.-Libyan relationship began to warm in 2003 when Libya renounced terrorism and weapons of mass destruction. It formally accepted responsibility for the Lockerbie bombing and paid billions of dollars in compensation for victims' families.