Revolutionary forces captured fighters close to Mutassim Gaddafi, one of fugitive leader Muammar Gaddafi's sons in his father's home town, but there was no confirmation that he had been captured, a Libyan spokesman said.
Jalal el-Gallal, a spokesman for the National Transitional Council in the eastern city of Benghazi, said his office had called commanders in the besieged city of Sirte and "so far as we are concerned there is no confirmation that Mutassim Gaddafi has been captured".
He was commenting following reports that the son had been seized, which prompted heavy celebratory gunfire in Tripoli and the eastern city of Benghazi.
Anti-Gaddafi fighters have been closing in on armed supporters of the fugitive leader in Sirte, the most important of two major cities yet to be cleared of loyalists more than two months after the fall of Tripoli.
Libyan officials have said they believe Mutassim Gaddafi and other high-level former regime figures are hiding in Sirte and that is the reason for the fierce resistance.
Mutassim was Libya's national security adviser and had a strong role in the military and security forces under his father's regime.
Libya's de facto leader, Mustafa Abdul-Jalil, said he expected to declare total victory in less than a week, as the International Committee of the Red Cross warned thousands of civilians were still trapped inside Sirte.
Gaddafi is still on the run and his supporters also hold the desert enclave of Bani Walid. But the transitional leadership says Sirte's capture will give them full control of the country's ports and harbours, allowing them to move forward with efforts to restore normality and establish a democracy.
Humanitarian workers are struggling to help civilians who lack food, clean water and other basic necessities. Red Cross staff evacuated 25 war-wounded and other patients, including a newborn baby in its incubator, from the main Ibn Sina hospital in the coastal city on Monday and Tuesday. Few doctors or nurses remained, the Red Cross said.
"The situation inside the hospital is very chaotic and distressing," the ICRC's Patrick Schwaerzler said. "When we arrived there we found patients with severe burns and shrapnel wounds. Some had sustained recent amputations. A few were half-conscious. They were lying among crowds of other people who were also asking us for help."