The only man convicted for the 1988 bombing of a Pan Am jet which killed 270 people when it blew up over the Scottish town of Lockerbie is drifting in and out of a coma, his brother said on Monday.

Abdelbaset Ali Mohmet al-Megrahi, who has terminal cancer, "is in and out of a coma," his brother Abdel Nasser told reporters outside the family home in a posh residential tree-lined street of the Libyan capital.

"His medicine was looted but he has new supplies now," said Abdel Nasser, who came out to speak to journalists who had massed outside the family home in the Dimashq neighbourhood.

Journalists were not allowed to enter the house.

Earlier, the CNN news network quoted Megrahi's son Khaled as saying his father is "surviving on oxygen and an intravenous drip" under the care of his family.

"We just give him oxygen. Nobody gives us any advice," Khaled told the US broadcaster.

"There is no doctor. There is nobody to ask. We don't have any phone line to call anybody."

It was not immediately possible to independently confirm Megrahi's condition.

Megrahi was said to have only three months to live when he was released from a Scottish jail on compassionate grounds on August 20, 2009.

He had served just eight years of a minimum 27-year sentence for his role in the bombing of Pan Am Flight 103 in December 1988.

Megrahi made his first public appearance in nearly two years in July at a gathering in support of embattled Libyan leader Moamer Kadhafi.

The fact that he has survived so long has provoked indignation in Britain and the United States, where some politicians have urged the rebel National Transitional Council (NTC) to extradite him.

But Megrahi's brother Abdel Nasser said he was not particularly concerned about the change of power in Tripoli, adding that the NTC official in charge of legal affairs "is an old friend of the family."

"The revolutionaries are Libyan and all the Libyans know that he is innocent," Abdel Nasser said.

US Republican presidential hopeful Mitt Romney urged Libya's transitional authorities "to arrest and extradite the mastermind behind the bombing of Pan Am 103... so justice can finally be done," in a statement August 23.

Several US senators issued similar statements.

The United States has no extradition treaty with Libya, and an NTC representative said any decision about Megrahi's future would have to wait until a new government is elected, which could take up to two years, the Los Angeles Times reported.

On the second anniversary of Megrahi's release, the Scottish government insisted that its decision to free him had been vindicated.

British Prime Minister David Cameron has criticised Megrahi's release as a "terrible mistake," and Deputy Prime Minister Nick Clegg has 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.