Abdelbaset al-Megrahi, a former Libyan intelligence officer, was convicted in the 1988 bombing of Pan Am Flight 103, in which 270 people were killed. He was released from prison by Scottish officials in August 2009 on compassionate grounds because of a terminal prostate cancer diagnosis.
Megrahi was reportedly in a coma by recently gave an interview to the Reuters news agency.
Victoria Nuland, a spokeswoman for the U.S. State Department, said Megrahi should have never been released from custody.
"He does seem to have made a miraculous recovery, doesn't he?" she said Monday during her regular briefing.
The Transitional National Council in Libya, she added, was looking at the case.
"My understanding is he remains at his house in Tripoli," Nuland said. "They have not made any firm decisions about where they will go with this but they know that we and the international community have concerns and believe that he should be behind bars."
Mohammed al-Alagi, the justice minister for the TNC, was quoted by CNN International as saying last week the case is closed.
"As Libyan justice minister, I believe this case is closed and a man can't be tried twice for the same alleged crime," he said.