The US voiced opposition to releasing a Libyan serving a life sentence in Scotland for the 1988 Lockerbie bombing that killed 270 people.
"We have made our views clear to the UK government, to other authorities, that we believe that he should spend the rest of his time in jail," State Department spokesman PJ Crowley said.
Abdel Basset al-Megrahi, 57, was convicted of the bombing of Pan Am Flight 103 over Lockerbie, Scotland in 2001 and received life imprisonment.
British media reported on Thursday that al-Megahi's release was imminent on compassionate grounds because he has been diagnosed with terminal prostate cancer. He would be allowed to return to his family in Libya.