A US senator has called for American officials to be given access to the Lockerbie bomber to assess his health.
Senator Robert Menendez has written to US Secretary of State Hillary Clinton urging her to ask Libya's National Transitional Council (NTC) to give American and international officials immediate access to Abdelbaset al-Megrahi.
He said Megrahi remains an "important source" of information on the bombing and should be questioned about it.
The Libyan is the only person convicted of the 1988 bombing of Pan Am flight 103, which killed 270 people.
He was released from a Scottish prison two years ago on compassionate grounds after being diagnosed with cancer and returned to Libya,
Footage showing him looking ill and apparently close to death was aired on US news channel CNN this week.
In his letter, Mr Menendez said it has always been known that Megrahi did not act alone.
He wrote: "While news reports suggest that Megrahi may be nearing death, he remains an important source of information about the Pan Am bombing."
He added: "We still do not know who ordered the bombing, who collected the intelligence to carry out the plan, who made the bomb and who - in addition to Megrahi - bears responsibility for this and other heinous attacks."
He said it is "crucial" that the NTC provides access to Megrahi and co-operates with any United States investigation into the Pan Am bombing.