Abdelbaset Ali Mohmet al-Megrahi, the Libyan convicted of the Lockerbie plane bombing, has been hospitalised in Tripoli in critical condition, a source close to his family said on Saturday.
"Abdelbaset has been in hospital since yesterday and his condition is critical," the source told AFP.
"He was admitted on Friday when his health became not so good," the source said, adding that Megrahi's relatives were at his bedside.
A Scottish court in 2001 convicted Megrahi of the 1988 bombing that killed 270 people, but he was released on compassionate grounds in 2009 and allowed to return to Libya.
Doctors said at the time that he had terminal cancer and only three months left to live.
Last August, after the revolution which toppled Moamer Kadhafi, brother Abdel Nasser told reporters outside the family home in a residential district of Tripoli that Megrahi was "in and out of a coma."
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Amid the lack of law and order after the revolt which brought armed fighters out onto the streets, his medicine had been looted and no doctors were available, the family said.
Megrahi had been greeted as a hero on his return to Kadhafi's Libya, after having served eight years of a minimum 27-year sentence for his role in the bombing of Pan Am Flight 103 in December 1988.
The fact that he has survived so long has provoked indignation in Britain and the United States.
On the second anniversary of the release of the former Libyan intelligence agent who has always maintained his innocence, the Scottish government insisted its decision to free him had been vindicated.
But British Prime Minister David Cameron has criticised the release as a "terrible mistake," and Deputy Prime Minister Nick Clegg said he would like to see him "back in jail behind bars."
Most of those killed in the bombing of the Boeing 747 jet headed from London to New York were Americans. All 259 passengers and crew were killed, along with 11 people on the ground.