Commanders for Libya's transitional authorities say they have captured ousted leader Col Muammar Gaddafi.
Unconfirmed reports say Col Gaddafi has been killed, and AFP obtained a mobile-phone image apparently showing his face covered in blood.
The reports came after transitional forces claimed control of Sirte, Col Gaddafi's birthplace.
The colonel was toppled in August after 42 years in power. The International Criminal Court is seeking his arrest.
Nato, which has been running a bombing campaign in Libya for months, said it carried out an air strike earlier on Thursday that hit two pro-Gaddafi vehicles near Sirte.
The head of the National Transitional Council (NTC) Mustafa Abdul Jalil is expected to give a national TV address soon.
Information Minister Mahmoud Shammam says fighters on the ground have told him that Col Gaddafi is dead.
Earlier, another NTC official told Reuters news agency: "He's captured. He's wounded in both legs."
"He's been taken away by ambulance."
AFP news agency quoted another NTC official, Mohamed Leith, as saying that Col Gaddafi had been captured in Sirte and was "seriously wounded" but still breathing.
A soldier who says he captured Muammar Gaddafi told the BBC the colonel had shouted: "Don't shoot!"
But NTC official Abdel Majid Mlegta told Reuters news agency that the former leader had been shot in the head and killed as he tried to flee.
Reuters also quoted another NTC commander, Abdul Hakim al-Jalil, as saying that Col Gaddafi's spokesman Moussa Ibrahim had been captured and the head of his armed forces, Abu Bakr Younus Jabr, had been killed.
None of the reports has been independently verified.
The BBC's Caroline Hawley in Tripoli says ships and cars have been sounding their horns in the capital and guns are being fired in celebration.
Earlier, NTC commanders in Sirte - about 360km (220 miles) east of Tripoli - said the city had been liberated.
"There are no Gaddafi forces any more," Col Yunus al-Abdali told Reuters. "We are now chasing his fighters who are trying to run away."
There was no confirmation from the NTC leadership.
But fighters in Sirte celebrated by firing in the air, and chanting "Allah akbar" ("God is great").
Interim government forces had been facing heavy resistance from snipers in the city, and used heavy artillery during its offensive. Thousands of civilians have fled.
The NTC has also suffered heavy casualties in the town of Bani Walid, south-east of Tripoli, in recent weeks.
On Monday the NTC said it had captured 90% of the town, including the centre.