Exclusive: As the Sri Lankan war approached its endgame, 130,000 civilians were trapped along a small strip of beach. An eyewitness recalls the bloodshed that followed and how civilians were targeted.

Sri Lankan soldiers. (Reuters)

This report contains details some readers may find distressing.

Over the last two years Channel 4 News has broadcast footage that the UN says constitutes "credible evidence of war crimes" in Sri Lanka.

In the final stages of 26 years of civil war between the Sri Lankan government and the Liberation Tigers of Tamil Eelam (LTTE, and better known as the Tamil Tigers), the United Nations estimated up to 40,000 civilians were killed.

"Fernando" was operating with Sri Lanka's 58 Division during the final assault. He has risked his life as well as the lives of his family to speak out about the horrors he witnessed. He told Channel 4 News that men, women, and children were actively targeted with small arms by government forces.

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"When I look at it as an outsider I think they're simply brutal beasts. Their hearts are like that of animals, with no sense of humanity," Fernando tearfully recalled.

"They shoot people at random, stab people, rape them, cut their tongues out, cut women's breasts off. I have witnessed all this with my own eyes. I have seen small children laying dead," he continued.

"I saw a lot of small children, who were so innocent, getting killed in large numbers. A large number of elders were also killed.

"They were shooting when a large number of civilians were crossing through a lagoon, including women and children. The soldiers were shooting at them. They were not Tiger cadres, just normal civilians. So yes, I saw normal civilians getting killed with my own eyes.

"I saw a family, a mother and three children. This small family was fleeing. As we were about to take them, one of the children was shot in the leg. The child fell. I carried that child with these hands. The mother was screaming."

Watch: Sri Lanka's Killing Fields on 4OD

"Fernando" said even the wounded were shown no mercy: "When they were at the hospital, one day I saw a group of six soldiers raping a young Tamil girl. I saw this with my own eyes."

"Fernando" was so horrified by what he saw that he described himself as "like a walking corpse".

Whereas the UN report on the final stages of the conflict focused on the shelling of civilians, the "Fernando" testimony is believed to be the first eyewitness account to suggest civilians were actively targeted by troops on the ground, a claim the Sri Lankan government denies.

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He claimed troops were allowed to act with impunity.

"If they wanted to rape a Tamil girl, they could just beat her and do it. If her parents tried to stop them, they could beat them or kill them. It was their empire.

"For the soldiers at the battlefront, their hearts had turned to stone. Having seen blood, killings and death for so long, they had lost their sense of humanity. I would say they had turned into vampires."

For the soldiers at the battlefront, their hearts had turned to stone. 'Fernando'

These inhumane acts, "Fernando" said, extended to acts of torture and mutilation.

"I saw the naked dead bodies of women without heads and other parts of their bodies.

"I saw a mother and child dead and the child's body was without its head."

Mass graves

The Sri Lankan government attempted to cover up such acts by burying the bodies in mass graves, according to "Fernando".

"Massive numbers of children, women and men were killed in the final stages of the war. When I say massive, in Puthumathalan alone, over 1500 civilians were killed.

"But they couldn't bury all of them. What they did was, they bought a bulldozer, they spread the dead bodies out and put sand on top of them, making it look like a bund.

"I saw 1500 bodies only in Puthumathalan, but I saw the same happen to more than 50,000 people like that."

Questioned on the accuracy of the numbers he cited, "Fernando" said: "In the final stage, all that I saw in Puthumathalan were dead bodies. When I entered the last place... it was totally full of dead bodies.

"They wanted to clear them that's why they brought that big vehicle. All they could do was just put sand on them. In some areas you couldn't go because there was such a terrible smell of decomposing bodies."

"They were just innocent Tamil civilians and did not belong to either warring party."

"Fernando" said he has cried for the suffering of those who died, and now he has decided to speak out because the world needs to know of what he described as the "heinous crimes" committed on one small strip of beach in May 2009.

"At the moment I’m ok – I've seen so many dead bodies, so many injuries, so many children, so many rape scenes, but I’m ok, that's why I opened my heart out to you," Fernando concluded.

The Sri Lankan government denies its troops committed war crimes.