Libya's new leaders will on Sunday declare liberation after the death of Muammar Gaddafi, paving the way for the formation of an interim government followed by the first free vote in 42 years.

The long-awaited declaration was being overshadowed, however, by raging controversy over the circumstances of Gaddafi's killing after he was captured alive during the fall of his hometown Sirte on Thursday.

National Transitional Council officials said the declaration would be made in the eastern city of Benghazi, cradle of the revolt, inspired by uprisings in Tunisia and Egypt, that began in February and, backed later by a NATO air war, saw Tripoli overrun in August.

The NTC had promised to proclaim the country's liberation once Sirte, Gaddafi's last bastion of support, had fallen.

Under the NTC's roadmap, an interim government would be formed within one month of the declaration, followed within eight months by elections for a constitutional assembly, the first democratic vote in Libya since Gaddafi seized power in a coup 42 years ago.

Parliamentary and presidential elections would be held within a year.

Interim leader Mustafa Abdel Jalil said an investigation was being conducted into the circumstances of Gaddafi's killing after several foreign governments and human rights watchdogs posed questions.

"We are dealing with the subject with transparency," Abdel Jalil told Al-Jazeera television.

Disquiet has grown internationally over how Gaddafi met his end after NTC fighters hauled him out of a culvert where he was hiding following NATO air strikes on the convoy in which he had been trying to flee his falling hometown.

Mobile phone videos show him still alive at that point.

Footage shows the former dictator, his face half-covered in blood, being dragged towards a vehicle by a frenzied crowd and forced on to the bonnet.

Those at the front push and shake him, pull him by the hair and hit him. At one point he appears to be trying to speak.

Subsequent footage shows him being hauled off the vehicle, still alive, and hustled through the screaming crowd, before he disappears in the crush and the crackle of gunfire can be heard.

NTC leaders are adamant he was shot in the head when he was caught ‘in crossfire’ between his supporters and new regime fighters soon after his capture.

Interim prime minister Mahmud Jibril told the BBC's Hardtalk programme that he would rather Gaddafi had survived.

"To be honest with you at the personal level I wish he was alive. I want to know why he did this to the Libyan people," he said. "I wish I were his prosecutor in his trial."

Jibril added that it would be ‘absolutely OK’ to carry out a full investigation under international supervision into the killing, as long as Islamic burial rules were respected.

Gaddafi's body has been stored in a vegetable market freezer in the eastern city of Misrata, drawing large crowds wanting to view the remains of the despot who ruled Libya with an iron fist for decades.

Military commanders in Misrata said on Saturday that no autopsy would be carried out on the body despite concerns over how he died.

As the rigid, bloodied, yellow corpses of Gaddafi and his son Mutassim lay on dirty mattresses on the metal floor of the glacial makeshift mortuary, hundreds of Libyans were allowed inside to view them.

A man identifying himself as Sadiq said he was only 18 when the former dictator took power in 1969.

"All my adult life I lived with this low life, this..." said the 60-year-old, who declined to give his last name, spattering curses against Gaddafi.

"But he is dead and I am happy," he said, laughing.

Russian Foreign Minister Sergei Lavrov said the "way his death happened poses an entire number of questions," and called for a probe.

UN human rights chief Navi Pillay also called for an investigation, as did Claudio Cordone, senior director at Amnesty International, who said that if Gaddafi "was killed after his capture, it would constitute a war crime and those responsible should be brought to justice."

Finland criticised Muammar Gaddafi's ‘violent death,’ warning that the manner of the ousted Libyan strongman's killing ‘serves no-one.’

And Gaddafi's widow, Safia, who fled to Algeria in August, called on the United Nations to investigate the circumstances of her husband's death, Syria-based Arrai television said.

Libya's wanted former intelligence chief Abdullah al-Senussi, meanwhile, surfaced in neighbouring Niger after apparently fleeing through the desert following the fall of the oasis town of Bani Walid on Monday in the penultimate battle of the conflict.

"The presence of Abdullah al-Senussi has been indicated in the far north of Niger," near the Libyan border, a government source in the capital Niamey told on Saturday.

Senussi is wanted by the International Criminal Court on charges of "crimes against humanity." The court leveled the same charges against Gaddafi and his son and longtime heir apparent Seif al-Islam.

Seif al-Islam too remains at large. NTC officials said that he too may have fled to Niger.