Libyans tried to save US Ambassador Chris Stevens after finding him in a locked, smoke-filled room following last week's attack on the US consulate in Benghazi, according to amateur and uncorroborated video footage obtained on Tuesday by AFP.

"Is there a doctor around? Does anyone know a doctor," a young man, among a crowd of people gathered around a body believed to be Stevens, is heard saying in the video footage, according to the translation offered.

Another person is seen checking the pulse of the victim.

In another scene, protesters are shown dragging a body out of a window and then placing it on the ground outside a building that has been burned by flames.

Ambassador Stevens and three other Americans were killed after the US consulate in Benghazi came under fire from rocket-propelled grenades on September 11 during a protest alledgedly against an anti-Islam film made in America.

The well-orchestrated attack which included advanced weaponry made it more likely that the attack was planned by organized terror groups to coincide with 9/11.

The White House promised Tuesday to follow an FBI probe into an attack on the US consulate in Benghazi wherever it led. "We have provided information about what we believe was the precipitating cause of the protests and the violence based on the information that we have had available," White House spokesman Jay Carney said. "The FBI is investigating, and that investigation will follow the facts wherever they lead."

US and Libyan officials have offered widely differing accounts of the assault, which coincided with the anniversary of the September 11, 2001 attacks in the United States.

The US ambassador to the United Nations, Susan Rice, echoing earlier accounts of the attack from the State Department, said Sunday it began with a spontaneous protest over an anti-Islamic video.

But Libya's parliament chief, Mohammed al-Megaryef, blamed the attack on a few foreign extremists who he said entered Libya from Mali and Algeria and pre-planned it with local "affiliates and sympathizers."

Fahid al-Bakush, who shot the video and shared it with AFP, said he and his friends arrived at the scene at around 12:15 am (2215 GMT September 11) after hearing there was an attack on the consulate.

"There were people defending the consulate and others trying to loot it," Bakush told AFP displaying images on his laptop of the crowd gathered at the burning premises.

Ahmed al-Faraj, a local journalist also at the scene, said that some men had pried open the gated balcony window and stumbled on the body inside.

"The ambassador was found by accident, when someone trod on him." Other accounts say that Stevens was killed by a rocket while trying to escape in a car.

"The people didn't know he was the ambassador, only that he was an American trapped in the room," he said. It is not certain that it is Stevens in the video and that the translation is accurate.

In the video, a voice is heard saying: "There is a dead man inside."

Moments later a small group men, carrying flashlights, is seen taking the body out of the building. "He is foreign," one person is heard saying.

"People tried to clear space so he could breathe and his eyes flickered," Ahmed Shamsi, who claimed that he witnessed those dramatic moments, told AFP. "He was breathing," insisted Abdelqader Fadel who edited the video and uploaded it online.

One picture provided by Bakush and his friends shows a man carrying the wounded American over his shoulder and heading towards a civilian car, in what they said was clear evidence they were trying to rush him to hospital to save him.

Ahmed Warfalli, who lives just a few doors down from the consulate, told AFP that police reinforcements arrived only two hours after gun and rocket fire shook the area. "They set off TNT, threw grenades and fired rockets," he said of the angry, armed mob.

He and other witnesses told AFP that they saw no peaceful banner-carrying or slogan-shouting protesters, describing what went down as a "surprise attack."

Seif Eddin Zoghbia was the general surgeon on duty at the Benghazi Medical Center when the ambassador was rushed in by strangers five hours later.

"At about 1 am, people bring in a patient who looked like a burn victim," he recalled.

"They were panicked. They wanted to save him at any cost. I came and checked his pulse but there was no pulse," added Zoghbia.

For the next half hour, doctors and nurses tried to revive the body to no avail, said Zoghbia, adding that the ambassador died of asphyxiation and that there were no signs of trauma on his body. He did not say where the asphyxiation occurred.

"At first I didn't know he was ambassador, or American," the medic said.