A doctor working with injured and displaced Tamils in northern Sri Lanka tells Channel 4 News that there may be as many as 20,000 amputees among those who fled attacks.

A wounded displaced Tamil child sleeps on the floor of a hospital in Chettikulam, northern Sri Lanka. (Getty)

Eyewitnesses interviewed during a week-long undercover investigation for Channel 4 News, told of thousands of civilian deaths as government forces advanced on the Tigers' final stronghold.

The deaths, they said, were the result of government shelling.

The Sri Lankan president and senior government ministers have repeatedly denied causing a single civilian death in what the government had desginated a "no-fire zone."

International aid agencies believe as many as 100,000 civilians may have been trapped inside, under a fierce bombardment.

"I think every day a thousand people were killed." Eyewitness

"I think every day a thousand people were killed," one of the very last to escape the tiny enclave told us. He was referring to the final two weeks of the conflict, during which the Sri Lankan government claimed not to have used heavy artillery.

"There were continuous shelling attacks," said the eyewitness. We have verified his identity as a man in a position of authority, but we are unable to reveal it.

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Members of Sri Lanka's ethnic Sinhalese majority also expressed deep misgivings about the fate of the island's Tamil minority now that the Tamil Tigers have been so decisively defeated.

Despite severe restrictions on access to camps for displaced civilians, evidence is emerging of maltreatment, despite a promise made by President Mahinda Rajapaksa in his "victory speech" to Sri Lanka's parliament.

"There is no one to represent the aspirations of the Tamil community." President Mahinda Rajapaksa

Speaking in the Tamil language, the president promised equal rights for Tamils and took "personal responsibility" for protecting them.

"Our heroic forces," he said, "have sacrificed their lives to protect Tamil civilians." A senior Roman Catholic priest, who has worked with the displaced in the heavily militarised northern town of Vavuniya, said the triumphalism of Sinhalese was "very sad" to witness".

There is no one to represent the aspirations of the Tamil community," he said. "They have a very uncertain future. It means they will live as a subjugated community, like under a foreign ruler."

One of the few senior members of the Tamil Tigers to have survived, Selvarasa Pathmanathan, its head of international relations, said yesterday that the rebels' struggle for a separate Tamil homeland would now continue from exile.

Exclusive interview: leader of the Tamil Tigers

"The legitimate campaign of the Tamils to realise their right to self-determination has been brutally crushed through military aggression," said a statement, released from an unspecified location.

Sri Lankans expressing concerns about the welfare and treatment of Tamil civilians - or questioning the army's version of its final assault on the Tamil Tigers - are branded unpatriotic, even traitorous.

Dr Wickramabahu Karunarathne, a left-wing politician and one of the few dissident voices in the Sinhalese community said: "The state media, every day, radio, papers, they classify us as traitors and they are rousing people against us."

Dr Karunaratne was the only interviewee prepared to talk openly on camera without having his face obscured and voice changed. One prominent Sinhalese journalist, Podala Jayantha, who had campaigned for greater media freedom, was abducted and severely beaten by unknown assailants, two weeks ago.

Amnesty International says that since 2006, 16 Sri Lankan journalists have been murdered, 26 assaulted, and many more detained. Foreign journalists have had their movements severely restricted and last month, our own accredited Asia Correspondent Nick Paton Walsh was deported.

Journalists and all independent observers were banned from the no-fire zone. Jonathan Miller

Journalists and all independent observers were banned from the no-fire zone, during and after the fighting, so no independent assessments have been made of government claims not to have killed civilians. It has blamed any deaths on the rebels.

Journalists have also been unable to enter the hospital in Vavuniya, where thousands of wounded civilians are being treated. Channel 4 News successfully smuggled a small camera into Vavuniya and interviewed a Tamil doctor there.

"It is most sure that the numbers without limbs are over 20,000. Most of the injuries causing loss of limbs were from shelling," he said. The doctor alleged that conditions in the camps for displaced people around Vavuniya, are poor and that malnutrition and disease are rife.

"We were all gathered together recently by the government and we were told that if we told the figures of the sick and why people are dying to the foreign NGOs that we will be killed for doing this."

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