A conservative French newspaper on Wednesday reported that Libyan leader Moamer Gaddafi's forces had killed over 10,000 people in the capital Tripoli since March.
The paper quoted an unnamed "diplomat close to the dossier" as saying the death toll in Tripoli in the three months since the uprising against Gaddafi's regime began was "several thousand dead, maybe more than 10,000."
The report did not give any breakdown for the estimate, which was questioned by New York-based rights watchdog Human Rights Watch.
"It's very difficult to estimate what is happening in Tripoli and in other government-controlled areas right now, but we have no indication to suggest the death toll is that high," Peter Bouckaert, HRW's Emergencies Director told the German Press Agency dpa.
While HRW "knows many people have been killed in the crackdown and many more disappeared into unknown detention facilities," Bouckaert estimated the death toll in Tripoli to be in the "hundreds," rather than in the thousands.
"We haven't received any information about large-scale massacre recently (in Tripoli)," he said.
HRW estimates the number of people killed nationwide since the uprising began in the eastern city of Benghazi in mid-February at "several thousand," including around 1,000 in the city of Misrurata, which was besieged by government forces for weeks.
Libya's opposition estimates the number of dead at 12,000.
The French government had yet to comment on Le Figaro's report, which comes as France and Britain prepare to escalate their intervention by deploying attack helicopters as part of the NATO-led campaign.
The helicopters are expected to be used to strike targets in Tripoli, where weeks of bombardments by coalition warplanes have failed to rout Gaddafi or prompt residents to join the uprising.
Le Figaro's sources accused Gaddafi of conducting a "scorched-earth policy, aiming to maintain terror in the capital and preventing any uprising."
HRW confirmed a climate of terror, saying it had reports of people being arrested for watching Al Jazeera or sending mobile phone text messages critical of the regime, and of men being tortured in front of their families before being disappeared. There were also reports of businesses being forced to remain open to maintain a semblance of nomality.