Vladimir Putin is the new hero of Russian democracy, courted by Western leaders. He is also responsible for one of the most savage atrocities since the Second World War. John Sweeney is the first journalist to reach the devastated village of Katyr Yurt, where 363 people were slaughtered by Russian forces

Her face burnt almost beyond recognition, she lies prone on her hospital bed and tells in a child's whispers of the day her mother, father, her two brothers, her sister and her cousin - among 363 people from the same village - were wiped out.

At eight years old, Taisa Abakarova is an eyewitness to the worst war crime in the savage campaign of Russia's acting President, Vladimir Putin, against the 'terrorist fighters' of Chechnya.

The village of Katyr Yurt, 'safe' in the Russian-occupied zone, far from the war's front line, and jam-packed with refugees, was untouched on the morning of 4 February when Russian aircraft, helicopters, fuel-air bombs and Grad missiles pulverised the village. They paused in the bombing at 3pm, shipped buses in, and allowed a white-flag convoy to leave - and then they bombed that as well, killing Taisa's family and many others.

The Observer , in a joint investigation with Channel 4's Dispatches , went to Katyr Yurt and saw what was left: a landscape as if from the Somme, streets smashed to matchwood, trees shredded, blood-stained cellars, the survivors in a frenzy of fear. The village was littered with the remains of Russian 'vacuum' bombs - fuel-air explosives that can suck your lungs inside out, their use against civilians banned by the Geneva Convention.

Local witnesses, astonished by the first visit by Western outsiders to their village, ringed west and east by special troops from the Russian secret police, the FSB, said they had counted 363 corpses piled two or three high in the street - 'so many you couldn't get a car past them' - before the Russians took many of the bodies away and dumped them in a mass grave.

Taisa has a cruelly burnt face, both hands burnt and bandaged, a broken right leg swathed in plaster, a left knee pinioned by iron bolts and internal bruising, and yet she wanted to tell us what happened. Taisa's father, Mansour, 45, a builder; her mother, Hava, 45, a school teacher; her brothers, Magomed, 14; Ruslan, 12; her cousin, Hava, eight; and her sister, Madina, six, were squashed into the family's black Volga saloon. She explained how the convoy left Katyr Yurt for what they hoped was safety. 'There was a white flag on our car, flying from a wooden stick,' she said. 'Then two planes came and they hit us and my dad and mum were sitting in front of us and my brother and me were sitting in the back seat. Then we were blown up. I fell to the mud in the ground.'

Taisa winced as her aunt, Tabarik Zaumajeva, swabbed the burnt skin around her eye. The aunt said: 'At night she is scared to close her eyes. She told me that she was afraid the whole picture would come back.'

The worst is that Taisa's aunt cannot bring herself to tell the little girl she is the only survivor of the seven people in the family car: 'I don't know how to tell her. If we tell her now, she wouldn't be able to bear it. She's already afraid to close her eyes at night. Last night she woke 10 times and we can't calm her down.'

Katyr Yurt, to the west of Grozny, was quiet, calm and untouched on the night of 3 February. But Grozny had fallen and Chechen fighters had fled Russian revenge. Some of them passed through Katyr Yurt. There is one story that two Russian soldiers were kidnapped or killed that night. On the morning of 4 February, all hell began.

Putin - who is widely expected to become President when Russia votes this month - has consistently denied human rights abuses in Chechnya. Putin's denials have mollified Western leaders, and only last month Foreign Secretary Robin Cook met him in Moscow and went out of his way to praise the ex-KGB secret policeman who gave out hunting knives to his troops on New Year's Day. Cook said of Putin: 'I found his style refreshing and open, and his priorities for Russia are ones that we would share.'

What follows is the evidence The Observer/Dispatches has obtained about what his forces did to the civilians of Katyr Yurt, evidence that might call into question the Foreign Secretary's endorsement of Putin's priorities 'that we would share'.

Rumissa Medhidova is 27, but her face is so sick with grief and horror she looks 30 years older. She became a widow on 4 February. 'All the Russians left the village and at around 10am they started to bomb.They used everything. In the centre of the village, not one house is left standing. In one family there were three children around their dead mother. They had been shot in the leg by Kalashnikovs. At half past four, they said: "We will give you two hours". They sent buses in with white flags.'

People rushed around to find white sheets or anything at all white to mark their cars. There was even time for a joke: 'I saw a cow with white on its horns and people were laughing.'

The convoy set off, each car showing a white flag, some cars showing two or three, packed with mainly women and children - the men held back, to make more room for children, said Rumissa. It headed west towards the town of Achoi Martan and safety. 'When we were on the open road, they fired ground-to-air rockets at us. It was a big rocket, not as big as a car. It was strange. It didn't explode once, it exploded several times. Every car had flags, how many cars I don't know. It was a mess, lots of them. They hit us without stopping.'

Could the Russians have mistaken the white-flag convoy for fighters? 'No, they couldn't mistake us. They knew very well there were a lot of refugees: 16,000 refugees and 8,000 locals in the village. In front of us was a big car full of children, not grown-ups. They burnt before my eyes.'

Her husband stepped out of the car and was killed by shrapnel. With her children, she ran from the carnage and made it Achoi Martan: 'I saw a lot of bodies but I don't know how many. There were a lot of people lying on the road. I didn't count them. I also saw different parts of burnt bodies collected in buckets.'

And then the cover-up began: 'The Russians wouldn't allow the people in the village to collect the bodies. They only allowed people on the fifth day to go and collect the bodies. When people arrived there, they asked: "Where are the bodies of our people?" The Russians said some had already been burnt. People say the Russians took the bodies and threw them in a mass grave.'

Another eyewitness, a wounded man of the killable age, said: ' They started bombing. Bombs, artillery. They were killing people.

'At our local school on the edge of the village there were Spetsnaz troops. They said: "We will give you a safe corridor." So everyone started to go towards Achoi Martan. Then they used rockets against us. Some say 350 refugees were killed, 170 from the village itself.'

Zara Aktimirova, 59, was looking after her mother, Matusa Batalova, 85, who had been hit by shrapnel. 'The fear was so terrible I do not have the words ... We were in a cellar. You could hear the vacuum bombs: "Whoosh, whoosh". We just got into this cellar and the whole house next to us was completely destroyed. If someone ran to the apartment block en-trance, snipers would fire and hit arms and legs.'

Later she and her mother passed along the road and saw the wreckage of the white-flag convoy: 'The cars were mangled up, like mincemeat. I didn't count the cars, I was carrying my mother. The convoy stretched maybe three kilometres. Every car was hit.' Her mother was dying.

Our fifth witness, a doctor, is glassy-eyed and dead-tired after operating on hundreds of patients without anaesthetics, medicines or electricity during the bombardment. He said: 'First they hit the village, then they gave civilians a corridor and they were shot. They didn't bring the dead to us, only those in agony. They brought 10 bodies, to check if they were alive or not: one baby among them, grown-ups, teenagers, some without both legs, burnt with traumas to the head, stomach. There were a lot of bodies in the village they didn't bring to us.'

Our sixth witness stood outside the ruin of his home in Katyr Yurt, leaning on two crutches. Rizvan Vakhaev, 47, was contemptuous of the dangers of speaking out. When two vacuum bombs fell outside his house, the blasts killed eight people: six women, a man and an 11-year-old boy outright; 10 more have died since. His wife is seriously injured, as are three of his children. His daughter-in-law died immediately.

He showed us where the children had been lying before the blast, and the remains of human intestines lying on the ground. The vacuum bomb is dropped by a parachute. As it falls to the ground, it releases a cloud of petrol vapour, which ignites, and the sky explodes. A US Defence Intelligence Agency study of 1993 reported: 'The kill mechanism against living targets is unique and unpleasant. What kills is the pressure wave, and more importantly, the subsequent rarefaction [vacuum], which ruptures the lungs.'

An old lady, our seventh witness, emerged from a hole in the ground, trembling. She put a piece of bread to her mouth: 'We didn't eat yesterday and today. It was like Doomsday. Helicopters, planes, three bombs fell when we were in the cellar. Three sons and one daughter died. Our fourth son is dying at the hospital.'

On our way out of the village, we stopped by the mosque. There we met our last eye-witness. He had made a tally of all the bodies before the Russians took them away, dragging some by chains from car bumpers. He had tried to wash the bodies, and give them some decency in the Muslim tradition. And the number of the dead? '363,' he said.

As we left the ruins of Katyr Yurt, we saw wreckage from what was left of the white-flag convoy: broken cars, twisted, charred metal, a boot lying in the mud. And then we heard a burst of machine-gun fire, an echo of 'the refreshing and open' language of Vladimir Putin.

'Dying for The President' will be shown on C4's 'Dispatches' on Thursday at 9.30pm.

john.sweeney@observer.co.uk